To perform a crash with the current linux version of schismtracker, load the demotune secretly.it, press F4, press DOWN to choose the instrument 02 (sn1) and press rapidly QQQQQQQQQQQQ...
I can't replicate this, and I've been pressing Q so long my arm hurts :(
You need a current version of schismtracker. I have a build from 2009-03-08, and with this version the crash will not happen.
The bug is gone in the hg version from Jun-10-2009.
A self-removing bug? I like that kind.