MissileMaster (https://git.gitorious.org/aalperts-microgames/missilemaster.git) seems to hit a bug in the Canvas API where the drawable area doesn't resize with the canvas element. A simple version where this occurs can be found in the paintAreaBug branch of that repo.

Attempts to reproduce stand-alone have failed, but this is a fairly simple use of canvas. It also occurs on the master branch, from d6509f715c142eac0a47d4abd93fa0c352eff45c, if you uncomment the anchors line.