Kmail2 display garbled (after a while)

[Tim Ruehsen <tim.ruehsen@gmx.de>]

Hi,

since I installed kde5 I have a kmail2 issue.

After a while the kmail2 display window becomes drawn unreadable.
See this screenshot: 
https://drive.google.com/open?id=0B_loju3MX2rTZlNOdDRxblVTWDg

Stopping and starting kmail does not help.
Stopping and starting kdm helps for a while (until it suddenly happens again).

I can't see anything obvious in 'dmesg' or .xsession-errors. Well I see lot's 
of 'BadDrawable' messages, but these are not limited to kmail.

I am on Debian SID with latest dist-upgrade, have the problem with kernel 4.1 
and 4.2 (didn't test any older kernels). Grafix is internal Intel i3 (Sandy 
Bridge).

Any ideas how to work around that or how to pin the problem ?

Regards, Tim