I'm running Chrome Version 15.
It seems that the character will keep moving in some direction even when the movement key is not being pressed. It doesn't happen all the time, only sometimes.
For example in this project I'm working on: Link you can be maneuvering your character, then he'll suddenly keep moving in one direction, even though your not telling him too, and it's stuck that way. Sometimes the whole time, and a refresh on the page is necessary to fix.