Created attachment 653900 [details]
dmesg output captured blindly from startx's vtty after startx exit

lspci reports onboard XGI Z7/Z9 (XG20 core) video
Xorg is using xf86-video-sis-0.10.8-2.1.x86_64 driver via xorg.conf and
display's native 1680x1050 mode (VESA 1024x768 without any xorg.conf): 

To reproduce:
1-login on a TW vtty in multi-user.target
2-startx plasma or icewm session
3-exit the plasma or icewm session normally

Actual behavior:
1-display put out of range
2-no action possible produces visual response before reboot effected

Expected behavior:
1-normal return to bash shell on vtty