There's a bug where, if you have a webkitTransitionEnd event listener on the page, and you run a transition on -webkit-transform, subsequent attempts to set the transform fail. The problem is that the animation isn't getting cleaned up off the GraphicsLayer, and so the transform change doesn't show up.
Created attachment 41339 [details] Patch
Comment on attachment 41339 [details] Patch r=mitz on irc
http://trac.webkit.org/changeset/49711