Bug 375268

When hovering over a GTK-window area producing a tooltip and quickly reach to hot corner to display the "Grid effect", Kwin freezes. One has a to go to Console (e.g. Ctrl+Atl+F1) to kill kwin_x11 to get control of the GUI again.

Step to reproduce:
- Have Kwin set to display Grid Effect on a hot corner (not tested with Windows Presentation, might or might not be reproducible with it)
- Open a GTK software (tested with LibreOffice and Gimp)
- Get a tooltip-displaying area close to the hot corner
- Reach quickly the hot corner to activate the effect while the tooltip is still displayed (my activation delays are set to 50ms, the default of 150ms might take to long to trigger the effect?)

Effects: The GUI freezes (apart from mouse) leaving you with no choice but to go into CLI, kill kwin_x11 (with "hard kill", e.g. -9 signal) and go back to GUI to restart kwin_x11.

Reproducible: Not always unfortunately. I have been able to reproduce the past 15 minutes, but now I don't seem able to re-trigger the bug anymore. The bug has been triggered quite a few times over the past weeks though.

Systems affected: Both OpenSuse Leap 42.2 and Tumbleweed (two different computers both using Intel HD Graphics), thus both very up-to-date regarding Plasma.