Created attachment 124122 [details]
Appearance of message pane
Upon waking up from sleeping the message pane is frequently not repainted properly - it's been like this for ages and ages. Changing message gets it fixed.
Are you using NVIDIA binary drivers?
Yes - wouldn't be that surprised if it is the problem but it only seems to affect kmail...
It should affect all OpenGL applications, except those where developers already added driver-specific workarounds. KMail uses OpenGL via QtWebEngine.
The workaround needs to be made in QtWebEngine, or ideally the NVIDIA driver fixed to not have this issue in the first place.