Steps to reproduce the problem:
1. Load this example: http://jsbin.com/orejoj/1/
2. Open up dev tools and inspect the div element with red outline
3. Change the 50% left position value to anything else
What is the expected behavior?
The background image should move accordingly
What went wrong?
The background image disappears and will only reappear when reloading the page
Created attachment 184727 [details]
Committed r140817: <http://trac.webkit.org/changeset/140817>