Look, I don't know much, but I think that happens because the computer has too many tasks at once. I say that because the same thing happened to me at Team Fortress 2, where doors disappeared or glitched out (and I have a problem in GE:S that a ge_facility door sometimes opens without the animation going, but since I believe that's on my end...). I tried to put antivirus in Silence Mode, stopped some subprocesses that doesn't go nowhere or that I never use (like Webcam) and that seemed to work it for me.
HOWEVER! Since the wrong movement could create problem on your PC, I suggest you wait for the next person. I do that because I don't have many options at my table and that miraculously worked. If a Dev says "That okay", then go for it; If not, then he'll probably have some thing or two to say.
