Starting Krusader in root mode results in blank grey rectangle with no panels, menus or icons. Would appreciate help or hints. It works on other machines I have installed it with the same OS etc - so this is probably not a bug but rather something missing in my configuration. There must be a missing library perhaps - but I am stumped. Krusader Version 2.4.0-beta3 kdesu installed Fedora 25 KDE Plasma 5.9.5 KDE Frameworks 5.34.0 QT v5.7.1 Kernel 4.11.3-200.fc25.x86 OS 64bit

The problem is related to compositing. Logged directly into KDE and disabled compositing. I then opened Krusader in root mode and it drew its display window normally. I re-enabled compositing and the reopened Krusader in root mode and it was fine. After logging out and in again - even rebooting to make certain - the correction was retained and Krusader root mode opened normally. However, I need to access this machine via VNC (I use TigerVNC as a client) and when I do so I still have the problem of Krusader in root mode opening as a blank grey rectangle and none of the routine described above remedies this.
When I attempt to open Krusader with kdesu from Konsole in the VNC window I get QStandardPaths: XDG_RUNTIME_DIR not set, defaulting to '/tmp/runtime-me'
and tail -f /var/log/messages has:
Jun 9 18:35:27 phoenix2 plasmashell: QXcbConnection: XCB error: 2 (BadValue), sequence: 29735, resource id: 123731973, major code: 142 (Unknown), minor code: 3
Jun 9 18:35:27 phoenix2 plasmashell: QXcbConnection: XCB error: 2 (BadValue), sequence: 29760, resource id: 94371846, major code: 142 (Unknown), minor code: 3
Jun 9 18:35:27 phoenix2 kwin_x11: QXcbConnection: XCB error: 3 (BadWindow), sequence: 61318, resource id: 41950064, major code: 3 (GetWindowAttributes), minor code: 0

Running Krusader directly as root (in VNC window) gives:
X Error: BadDrawable (invalid Pixmap or Window parameter) 9
Major opcode: 62 (X_CopyArea)

Video Card is a GeForce GT 640. Driver is nouveau

Would appreciate advice.

SOLVED
As noted in the previous post I discovered that the problem was related to compositing and this was resolved in a normal desktop session by disabling compositing - opening krusader in root mode (success) and then re-enabling compositing after which Krusader opens successfully each time. To resolve this in a VNC session requires opening krusader with
kdesu QT_X11_NO_MITSHM=1 krusader
This can also be added as a user action in the Krusader settings Konfigurator menu and a meta key configured for faster access.
This will apply to other applications that open with a blank grey window using kdesu in a vnc session.
Hope this help others who encounter this problem.

Thanks for sharing!

There can also be other problems when running Qt5 applications as root.
A general solution is (hopefully):
su -l -c "QT_X11_NO_MITSHM=1 export DISPLAY=:0 && dbus-launch krusader"