Need hints trying to locate a compositing issue.

[Nikolai Zhubr]

Hi devels,

Sorry if this is not the best place to ask, feel free to point me to a 
better one if necessary.

I'm using KDE 4.11 which came with my opensuse 13.2. Sure it is a pretty 
old system but it still does its job fine every day and I plan to keep 
it for some while. I've made quite a lot of updates to support newer 
hardware etc.

Now to the point. I have desktop effects enabled (desktop cube, woobly 
windows, etc) for years and had nothing wrong with it. The video adapter 
is Intel HD (builtin), OpenGL works fine. Now I've found a reliably 
reproducable issue. When I connect to a remote windows box using RDP and 
start picture/fax viewer in it and then scroll the picture up/down 
rapidly several times inside this remote picture/fax viewer while 
simultaneously moving mouse around aggressively, an artifact appears. It 
looks as if 2 flip-pages of window contents buffer being repeatedly 
interchanged as mouse approaches control buttons (and some small 
repainting therefore needs to happen) AND one of this pages then 
exhibits a vertically misplaced portion of the picture, so part of the 
window looks "flashing" rapidly until I stop moving the mouse. It feels 
a bit like maybe some memory corruption so I'd like to try find and fix it.
The issue does not happen with Desktop Effects disabled or set to 
XRender, therefore I suppose the RDP application is not to blame. 
Obviously it is related to OpenGL and compositing and vertical block 
movement. Now my suspect list is the following:

1. kernel 4.14.174 - buggy drm module?
2. libdrm 2.4.67 - buggy library?
3. Mesa 11.2.2 - buggy library?
4. xorg 1.16.1 - buggy X?
5. intel X module 48.20200205.fc33 (from Fedora core 33) - buggy intel 
driver?
6. kwin 4.11.20 - buggy compositor?

So pretty large list, and I'm not sure how to better dig it further. Any 
hints greatly appreciated. Maybe it is a known issue already?

Thanks.

Regards,
Nikolai