Extreme FPS drops with 1.0.3c -- from 100 to 10 in a matter of seconds.

I just updated from 1.0.1c to 1.0.3c and have run into an issue that makes the game unplayable: Just running in a circle with my character (a paladin/angel) will make FPS drop from 100 to 10ish within 30s. This happens after every load, so reloading is not an option. It's also not something basic with my settings, I think, since I never witnessed this with the old version.

Details that may or may not matter:

• Switching to another character will make the FPS jump back up again, but going back to my pally makes the fps drop directly down to where it was before the switch (so no restart at 100, but back to whatever it was).

• Area size or NPC density does not matter. The FPS drop will occur regardless.

• Neither my CPU nor my GPU are showing excessive load. They're both <50%.