I've found a bug that appears to occur in Chrome, but not firefox.
When you have an object that has been assigned platform behaviour, then click with the left mouse button at exactly the same time as pressing one of the movement arrow keys then the object will keep moving indefinitely until you press the arrow key again.
Bit of a precise bug this, but quite frustrating =P
Here is a capx showing an example:
Should also note that I couldn't see any errors in the console window for chrome =)