Avast 5's Behavior Shield Slowing Down PC

When I enable AVAST 5's Free Edition's Behavior Shield it causes flash (in chrome and firefox) to skip, both video and audio, and also cause the cursor to skip around. Similar problems sometimes occur in games (like Mass Effect 2 or COD MW2). When I disable the Behavior Shield everything works perfectly again immediately. The problem doesn't appear to spread to other applications, so when I minimize, close or otherwise unfocus that application the cursor moves around fine on the desktop or another window.

System Specs: Win XP, 4GB(3.4)GB DDR2 Ram, Intel Cure 2 Duo E6700 2.67GHz.

I mean, it's not top of the line, but I feel it should be more than enough to run Avast in full. It's even a clean XP install with recent virus scans (both avast boot-scan and safe-mode malwarebytes scan).

Any help is appreciated.
Thank you.