My desktop is native at 1920x1200.

I started dota2.
I switched in the options the resolution from 1920x1200 to 1200x800-->dota2
display corruption.

Nearly blind, namely by guessing the location of the buttons on the screen, I
was able to quit dota2 to the desktop (non compositing xfce4 desktop).

The desktop display is not corrupted.

If I start again dota2, the resolution will be fine at 1200x800.

It is the same pb if I switch on/off vsync in dota2 options.