You can see a demonstration here: http://dl.dropbox.com/u/41931267/Mousekeyboardbug/index.html
You can see it in the demo, but basically when clicking and moving, the player sometimes gets 'stuck' moving in a direction.
This is not a fault of scirra's. However to encourage Google Chrome to fix this problem, many of us need to report the bug.
You can do that here: http://code.google.com/p/chromium/issues/entry
I know this issue is of importance to many in the community.
EDIT: here's my bug report, for any reason ;)
Click the star icon on the top left of the screen (when logged in with gmail) to vote for this bug getting fixed !!!
We need as many votes as possible to bring the issue to Chrome's attention!
Click this star so it looks like on the screenshot.