More info:
I tried again with juggler3d and it crashed first time upon exit. flurry also
triggered the crash on exit.
So I now suspect that antmaze isn't problematic - it is not starting a
screensaver that causes the crash, but closing one. As I switched screensavers
randomly in xscreensaver-demo, I just by chance clicked on antmaze when I had a
problematic screensaver selected previously.