Odd -fast effects?

Hmm, I've been running map07 of Vanguard, both regular and -fast (regular before, -fast now), and I have no idea what's going on but it really seems as if arachnotrons survive 3-4 rocket hits way more often in -fast.

http://www.mediafire.com/download/z874hbvomrtqw9m/vg07_wtfthisalwayshappens.lmp (Recorded in prBoom+ 2.5.1.4 -cl 9.)

How much damage are these rockets doing?

Sample size is pretty big. I aborted close to no regular runs because of this, yet I'm aborting half of my -fast runs because one of these spiders is surviving three or even four direct hits. Very often in the way you see in that demo. Really annoying.

It could be the way the difference in movement carries them into the blockmap (i.e., more likely to shoot and stay put in the weird blockmap areas), but it happens even when the first or second spider doesn't get off a shot.

Maybe this bug takes effect there, except applied to rocket splash damage instead of barrel splash damage?