That's crashing in the driver code that measures temperature. Are you using another app to adjust temperature/fanspeed at the same time? Theoretically they can fight over it. Disabling the other app if that's so might help. Not making cgminer adjust fanspeed/gpuspeed might help, or disabling all control/monitoring entirely with --no-adl should help if all else fails.
No, I don't use any other adjustment software. Your diagnosis is right: if I don't export DISPLAY, just COMPUTE, I get no fanspeed/temperature monitoring, and there is no error on quit. But I'd really like to have these features... summer is coming.
What I can't understand is why driver fails when I quit the program, and works perfectly fine while it is still running - it adjusts the fanspeed and engine clock to match my target temperature.
PS. You're great, -ck. Thanks for all your work:)