I am running KDE version 4.12.4 with armhf Debian sid on a Samsung Chromebook XE303c12, using the fbdev Xorg driver. Whenever I open the Panel Tool Box and select Add Widgets, it stops registering any mouse actions at all. I am unable to click on the widgets, the scroll bar, and the buttons along the top, including the "x". Despite this, I am still able to drag the widgets already on the panel around, and the Panel Tool Box itself works fine (i.e. resizing the panel, etc.) Also, it continues to receive keyboard input, as I can type in the widget search box. This malfunction also occurs in certain other widgets such as the battery indicator (unable to control the display brightness setting or select "Enable Power Management") and the "Available Devices" menu, whereas others, such as the calendar and volume control, work perfectly fine. Perhaps this has to do with the mouse input driver? (I am currently using mtrack)? Does anyone have any suggestions as to what might be the cause of this?

Thanks in advance.

This sounds like a focusing issue. Are you using Plasma Active or Plasma Desktop on this system?

I am running Plasma Desktop. When I have time, I will check if replacing kwin with fluxbox or openbox makes any difference.

Okay. One thing you could try is disabling/enabling compositing to see if that has any effect.

apparently the widget box (or anything in plasma-desktop) grabs input (mouse and keyboard) and forgets to release it.

You can (probably) add debug options to the ServerFlags section of your xorg.conf (code has been deactivated, removed, readded - so it depends on your Xorg version whether it works)

Option "AllowDeactivateGrabs" "boolean"
This option enables the use of the Ctrl+Alt+Keypad-Divide key sequence to deactivate any active keyboard and mouse grabs. Default: off.

Option "AllowClosedownGrabs" "boolean"
This option enables the use of the Ctrl+Alt+Keypad-Multiply key sequence to kill clients with an active keyboard or mouse grab as well as killing any application that may have locked the server, normally using the XGrabServer(3x) Xlib function. Default: off.
Note that the options AllowDeactivateGrabs and AllowClosedownGrabs will allow users to remove the grab used by screen saver/locker programs. An API was written to such cases. If you enable this option, make sure your screen saver/locker is updated.

Firstly, neither disabling compositing nor using different WMs had any effect. I attempted to enable the debugging settings, but using the specified shortcuts did not seem to achieve anything (perhaps Debian's binaries aren't compiled with debugging support?). Considering this is exclusively a mouse issue (I can close the menus with ESC and type in the text box), I wonder whether the mouse input driver has any effect.

I have attempted replacing mtrack with synaptics, but once again this had no effect. As a side note, is it possible to control these Plasma menus/widgets using the keyboard?

My first poet here. I'm experiencing the same problem with an Ubuntu 14.04 KDE installation on an ARMHF Cubox-i. I can't left lick (but can right click) on widgets. If I reverse the mouse (right handed to left) then it's the right click that doesn't work (the same functionality). I've tried disabling effects but nothing. Solving this is above my payscale unless someone else can help.

Is there a way to manage widgets without the use of the mouse?

Using the Keyboard to control the mouse also doesn't work, interestingly. KDE, on ARM, simply won't acknowledge "left click".

Have filed a Bug Report: https://bugs.kde.org/show_bug.cgi?id=341184

If anyone else has this problem, please add yourself to the bug report.