Debian Multimedia :: Xscreensaver Randomly Crashes X

My supposedly stable system was crashing. The problem was one or more specific screensavers--xscreensaver, the display manager (lightDM), and X itself are innocent as far as I can tell.

I'm on a Thinkpad T400 with Debian Jessie (8.4)/MATE/lightDM. I have libreboot and not proprietary BIOS. I like variety, so in addition to installing xscreensaver itself (the unofficial patched jessie version without the "out of date" nag, which I got from https://angband.pl/debian/pool/main/x/xscreensaver/), I also installed some extras from the official repository (xscreensaver-gl-extra, xscreensaver-data-extra, xscreensaver-screensaver-bsod). I enabled all the installed screensavers and asked xscreensaver to randomly cycle through them.

To my dismay, after variable lengths of time (usually within 20-60 minutes), when a random screensaver has been on for a little while (I'm guessing as it's about to go to the next random one), X crashes to a black screen. The only way to make the black screen go away is to kill X (which I mapped to Control + Alt + Backspace) then log back in. There are no useful logs anywhere except some cryptic IO error 11 entry in ~/.xsessionerros.

Now for the troubleshooting:

1) First I tried installing a more up-to-date version of xscreensaver (5.34-2), which I grabbed from the sid repository. This didn't work--same problem as described above. Therefore, I went back to the patched version for jessie (5.30-1 from angband.pl).

2) To exclude that the lightDM middleman was the problem, I disabled it and was logging in with startx. Problem did not go away. (I then rigged systemd to log me in automatically and for startx to run automatically once I'm logged in--who needs middlemen?)

3) To exclude screensavers butting heads, I uninstalled mate-screensaver and disabled anything from X that could be interfering (by running these commands in a startup script: xset -dpms; xset s 0 0; xset s noblank; xset s off). Problem did not go away. I kept this startup script nevertheless.

4) Finally, to exclude individual xscreensaver module(s) being the problem, I unchecked them all. Then I wrote down the names of my 20 favorite modules (which include some from gl-extra, some from data-extra, and bsod) and tested them in small batches, running xscreensaver with only 5 favorites checked at a time. After testing four batches of 5 and witnessing all 20 favorites both display and load without any X crashes, I went ahead and selected all 20 favorites. I left the laptop on overnight and in the morning (about 12 hours later) it's still going strong.

One or more particular xscreensaver modules are crashing X, probably at the time they are being loaded to be the next one to show. I think I already spent enough time on this, so don't really care to identify +/- troubleshoot the offending modules.