I manage two workstations which were updated to suse leap 42.1 at the same
time. Both utilize kde with plasma 5.

I wish to have both shade windows with a double click.

(The files /etc/sddm/conf of both are identical.)

Output of qdbus for both follows. The first output shows Work1 for which
setting Titlebar Actions to Shade works correctly. The 2nd output shows Work2
for which Titlebar Actions set to Shade produces no effect.
___________________________________________________________________________
Work1:
KWin Support Information:
The following information should be used when requesting support on e.g. http://forum.kde.org.
It provides information about the currently running instance, which options are used,
what OpenGL driver and which effects are running.
Please post the information provided underneath this introductory text to a paste bin service
like http://paste.kde.org instead of pasting into support threads.

==========================

Version
=======
KWin version: 5.4.2
Qt Version: 5.5.0
Qt compile version: 5.5.0
XCB compile version: 1.11.1

Operation Mode: X11 only

Build Options
=============
KWIN_BUILD_DECORATIONS: yes
KWIN_BUILD_TABBOX: yes
KWIN_BUILD_ACTIVITIES: yes
HAVE_WAYLAND: yes
HAVE_WAYLAND_EGL: yes
HAVE_WAYLAND_CURSOR: yes
HAVE_XKB: yes
HAVE_INPUT: yes
HAVE_DRM: yes
HAVE_GBM: yes
HAVE_X11_XCB: yes

X11
===
Vendor: The X.Org Foundation
Vendor Release: 11702000
Protocol Version/Revision: 11/0
SHAPE: yes; Version: 0x11
RANDR: yes; Version: 0x14
DAMAGE: yes; Version: 0x11
Composite: yes; Version: 0x4
RENDER: yes; Version: 0xb
XFIXES: yes; Version: 0x50
SYNC: yes; Version: 0x31
GLX: yes; Version: 0x0

Decoration
==========
Plugin: org.kde.breeze
Theme:
Blur: 0
onAllDesktopsAvailable: true
alphaChannelSupported: true
closeOnDoubleClickOnMenu: false
decorationButtonsLeft: 0, 2
decorationButtonsRight: 6, 3, 4, 5
borderSize: 3
gridUnit: 10
font: Oxygen-Sans,10,-1,0,50,0,0,0,0,0
smallSpacing: 2
largeSpacing: 10

Options
=======
focusPolicy: 1
nextFocusPrefersMouse: true
clickRaise: true
autoRaise: false
autoRaiseInterval: 750
delayFocusInterval: 300
shadeHover: false
shadeHoverInterval: 250
separateScreenFocus: false
placement: 4
focusPolicyIsReasonable: true
borderSnapZone: 10
windowSnapZone: 10
centerSnapZone: 0
snapOnlyWhenOverlapping: false
rollOverDesktops: true
focusStealingPreventionLevel: 1
legacyFullscreenSupport: false
operationTitlebarDblClick: 5009
operationMaxButtonLeftClick: 5000
operationMaxButtonMiddleClick: 5015
operationMaxButtonRightClick: 5014
commandActiveTitlebar1: 0
commandActiveTitlebar2: 30
commandActiveTitlebar3: 2
commandInactiveTitlebar1: 4
commandInactiveTitlebar2: 30
commandInactiveTitlebar3: 2
commandWindow1: 7
commandWindow2: 8
commandWindow3: 8
commandWindowWheel: 31
commandAll1: 10
commandAll2: 3
commandAll3: 14
keyCmdAllModKey: 16777251
showGeometryTip: false
condensedTitle: false
electricBorderMaximize: true
electricBorderTiling: true
electricBorderCornerRatio: 0.25
borderlessMaximizedWindows: false
killPingTimeout: 5000
hideUtilityWindowsForInactive: true
inactiveTabsSkipTaskbar: false
autogroupSimilarWindows: false
autogroupInForeground: true
compositingMode: 2
useCompositing: true
compositingInitialized: true
hiddenPreviews: 1
unredirectFullscreen: false
glSmoothScale: 2
colorCorrected: false
xrenderSmoothScale: false
maxFpsInterval: 16666666
refreshRate: 0
vBlankTime: 6000000
glStrictBinding: true
glStrictBindingFollowsDriver: true
glCoreProfile: false
glPreferBufferSwap: 97
glPlatformInterface: 1

Screen Edges
============
desktopSwitching: false
desktopSwitchingMovingClients: false
cursorPushBackDistance: 1x1
timeThreshold: 150
reActivateThreshold: 350
actionTopLeft: 0
actionTop: 0
actionTopRight: 0
actionRight: 0
actionBottomRight: 0
actionBottom: 0
actionBottomLeft: 0
actionLeft: 0

Screens
=======
Multi-Head: no
Active screen follows mouse: yes
Number of Screens: 1

Screen 0:
---------
Name: DVI-0
Geometry: 0,0,1920x1200
Refresh Rate: 59.9502


Compositing
===========
Compositing is active
Compositing Type: XRender

Loaded Effects:
---------------
screenshot
kwin4_effect_windowaperture
highlightwindow
kwin4_effect_dialogparent
dashboard
kscreen

Currently Active Effects:
-------------------------

Effect Settings:
----------------
screenshot:

kwin4_effect_windowaperture:

highlightwindow:

kwin4_effect_dialogparent:

dashboard:
brightness: 0.5
saturation: 0.5
blur: false

kscreen:
___________________________________________________________________________
Work2:
KWin Support Information:
The following information should be used when requesting support on e.g. http://forum.kde.org.
It provides information about the currently running instance, which options are used,
what OpenGL driver and which effects are running.
Please post the information provided underneath this introductory text to a paste bin service
like http://paste.kde.org instead of pasting into support threads.

==========================

Version
=======
KWin version: 5.4.2
Qt Version: 5.5.0
Qt compile version: 5.5.0
XCB compile version: 1.11.1

Operation Mode: X11 only

Build Options
=============
KWIN_BUILD_DECORATIONS: yes
KWIN_BUILD_TABBOX: yes
KWIN_BUILD_ACTIVITIES: yes
HAVE_WAYLAND: yes
HAVE_WAYLAND_EGL: yes
HAVE_WAYLAND_CURSOR: yes
HAVE_XKB: yes
HAVE_INPUT: yes
HAVE_DRM: yes
HAVE_GBM: yes
HAVE_X11_XCB: yes

X11
===
Vendor: The X.Org Foundation
Vendor Release: 11702000
Protocol Version/Revision: 11/0
SHAPE: yes; Version: 0x11
RANDR: yes; Version: 0x14
DAMAGE: yes; Version: 0x11
Composite: yes; Version: 0x4
RENDER: yes; Version: 0xb
XFIXES: yes; Version: 0x50
SYNC: yes; Version: 0x31
GLX: yes; Version: 0x0

Decoration
==========
Plugin: org.kde.breeze
Theme:
Blur: 0
onAllDesktopsAvailable: true
alphaChannelSupported: true
closeOnDoubleClickOnMenu: false
decorationButtonsLeft: 0, 2
decorationButtonsRight: 6, 3, 4, 5
borderSize: 2
gridUnit: 10
font: Oxygen-Sans,10,-1,5,50,0,0,0,0,0
smallSpacing: 2
largeSpacing: 10

Options
=======
focusPolicy: 1
nextFocusPrefersMouse: true
clickRaise: true
autoRaise: false
autoRaiseInterval: 750
delayFocusInterval: 300
shadeHover: false
shadeHoverInterval: 250
separateScreenFocus: false
placement: 4
focusPolicyIsReasonable: true
borderSnapZone: 10
windowSnapZone: 10
centerSnapZone: 0
snapOnlyWhenOverlapping: false
rollOverDesktops: true
focusStealingPreventionLevel: 2
legacyFullscreenSupport: false
operationTitlebarDblClick: 5009
operationMaxButtonLeftClick: 5000
operationMaxButtonMiddleClick: 5015
operationMaxButtonRightClick: 5014
commandActiveTitlebar1: 0
commandActiveTitlebar2: 30
commandActiveTitlebar3: 2
commandInactiveTitlebar1: 4
commandInactiveTitlebar2: 30
commandInactiveTitlebar3: 2
commandWindow1: 7
commandWindow2: 8
commandWindow3: 8
commandWindowWheel: 31
commandAll1: 10
commandAll2: 3
commandAll3: 14
keyCmdAllModKey: 16777251
showGeometryTip: false
condensedTitle: false
electricBorderMaximize: true
electricBorderTiling: true
electricBorderCornerRatio: 0.25
borderlessMaximizedWindows: false
killPingTimeout: 5000
hideUtilityWindowsForInactive: true
inactiveTabsSkipTaskbar: false
autogroupSimilarWindows: false
autogroupInForeground: true
compositingMode: 1
useCompositing: true
compositingInitialized: true
hiddenPreviews: 1
unredirectFullscreen: false
glSmoothScale: 2
colorCorrected: false
xrenderSmoothScale: false
maxFpsInterval: 16666666
refreshRate: 0
vBlankTime: 6000000
glStrictBinding: true
glStrictBindingFollowsDriver: true
glCoreProfile: false
glPreferBufferSwap: 101
glPlatformInterface: 1

Screen Edges
============
desktopSwitching: false
desktopSwitchingMovingClients: false
cursorPushBackDistance: 1x1
timeThreshold: 150
reActivateThreshold: 350
actionTopLeft: 0
actionTop: 0
actionTopRight: 0
actionRight: 0
actionBottomRight: 0
actionBottom: 0
actionBottomLeft: 0
actionLeft: 0

Screens
=======
Multi-Head: no
Active screen follows mouse: yes
Number of Screens: 1

Screen 0:
---------
Name: DVI-I-1
Geometry: 0,0,1920x1200
Refresh Rate: 59.9502


Compositing
===========
Compositing is active
Compositing Type: OpenGL
OpenGL vendor string: nouveau
OpenGL renderer string: Gallium 0.4 on NV84
OpenGL version string: 3.0 Mesa 11.0.2
OpenGL platform interface: GLX
OpenGL shading language version string: 1.30
Driver: Nouveau
GPU class: G80/G90
OpenGL version: 3.0
GLSL version: 1.30
Mesa version: 11.0.2
X server version: 1.17.2
Linux kernel version: 4.1.12
Direct rendering: Requires strict binding: yes
GLSL shaders: yes
Texture NPOT support: yes
Virtual Machine: no
OpenGL 2 Shaders are used
Painting blocks for vertical retrace: no

Loaded Effects:
---------------
zoom
screenshot
minimizeanimation
presentwindows
kwin4_effect_dialogparent
highlightwindow
dashboard
startupfeedback
kscreen

Currently Active Effects:
-------------------------

Effect Settings:
----------------
zoom:
zoomFactor: 1.2
mousePointer: 0
mouseTracking: 0
enableFocusTracking: false
followFocus: true
focusDelay: 350
moveFactor: 20
targetZoom: 1

screenshot:

minimizeanimation:

presentwindows:
layoutMode: 0
showCaptions: true
showIcons: true
doNotCloseWindows: false
ignoreMinimized: false
accuracy: 20
fillGaps: true
fadeDuration: 150
showPanel: false
leftButtonWindow: 1
rightButtonWindow: 2
middleButtonWindow: 0
leftButtonDesktop: 2
middleButtonDesktop: 0
rightButtonDesktop: 0

kwin4_effect_dialogparent:

highlightwindow:

dashboard:
brightness: 0.5
saturation: 0.5
blur: false

startupfeedback:
type: 1

kscreen:
__________________________________________________________________________

As best I can tell, the only significant difference between the two qdbus
outputs it that Work1 uses XRender whereas Work2 uses OpenGL.
Work2:>lspci | grep VGA
02:00.0 VGA compatible controller: NVIDIA Corporation G84GL [Quadro FX 1700] (rev a1)
Work2>egrep -i " connected|card detect|primary dev|Setting driver" /var/log/Xorg.0.log
[ 93513.498] (II) NOUVEAU(0): Output DVI-I-1 connected

Can the difference of compositors cause the problem? I must be missing
something else.

jim

Simply try with suspended compositor (SHIFT+Alt+F12)
While I can't imagine how a particular compositor would break actual shading, but it might be simply a visual thing (ie. the framebuffer isn't updated) - can you interact with the supposed-to-be-but-not-really shaded window?

> OpenGL vendor string: nouveau
nvidia blob (legacy driver, iirc 304.xxx) isn't an option?

I can interact with all windows, per normal.

Bizarrely, immediately after reading your reply, something that I did in an application crashed the OS -- something
that's only happened to me in roughly 20 yrs! -- so I had to do a cold boot.

With that reboot, the problem appears to be gone: windows shade with double click when asked. Something more than system settings
was messed up, I suppose.

Since upgrading to plasma 5 with suse leap 42.1, when closing individual windows, I *frequently* get error messages that plasma 5 has crashed.

Thanks for your suggestion -- I may yet need it
jim

Next time you run into this, try whether *any* doubleclick action works on the titlebar (maximizing etc.)
*something* in the system seems to mess doubleclick intervals, see https://bugs.kde.org/show_bug.cgi?id=345473

Bug cited above was fixed, but with Plasma 5.8.6 (installed with SuSE OpenLean 42.2) the exact problem returns.
Double clicking often but not always produces no effect (should un/shade). Repeatedly double clicking eventually
shades. Moving cursor around to different points in the window border has no effect.