https://bugs.freedesktop.org/show_bug.cgi?id=65192
--- Comment #4 from Michel Dänzer michel@daenzer.net --- (In reply to comment #3)
R600_HYPERZ=0 /usr/bin/xscreensaver-demo
and switching between screensavers crashed as often as without R600_HYPERZ=0.
Beware that AFAIK the screensaver hacks aren't spawned from the xscreensaver-demo process but from the xscreensaver daemon process. Did you confirm that the latter saw the environment variable?