FPS Slowdown Concerning Boulder

[TheCollective15]

I am near the mine

Spoiler below!

where you first discover the spiders, the mine that is particuarly steamy and moist. Normally you would wander in deeper, until you hear the spider eggs cracking, and then you would take a boulder and roll it up to barricade the little arachnids. This works fine with the very first boulder, but once you come across the second one (near the broken paraffin lamp) and roll it near the entrance, the FPS plummets terribly, until you actually move the boulder right next to the entrance, when the FPS becomes normal again. This has caused me stress at least the first time I tried the level, because I was not expecting the screen to slow down, and I actually pushed the rock the wrong way during the confusion...stupid spiders...

I have an Intel Core 2 Duo E6600, 2Gb RAM, and a GeForce 7900 GS, so it is not from older hardware...and yes, I have the newest drivers installed, Thomas.

I don't think I have heard this specific bug mentioned anywhere else; if it is elsewhere on the forums, forgive me.