If you see the floor freaking out when you get to the room after the classroom, or just any room in general, you can fix it by doing this:

Go into the games directory and open the cfg folder. Then open the game.cfg file in notepad or whatever editor you like and change the ;_ Floor section to this:

;_ Floor
WholeFloorTex=1
FloorBufferNumVertices=2048
FloorBufferNumFaces=1536
SysMemFloor=1
FloorSize=100

This seems to fix it, though I have only just started the game so I don't know how consistent it is. Hope this helps!