Specifying a CSS Transition on background-position has no effect. See URL for testcase example of a background image moving from 40px 40px to 80px 80px on :hover but there's no transition being applied at all.
*** Bug 23984 has been marked as a duplicate of this bug. ***
Created attachment 29735 [details] Patch, changelog, testcases
http://trac.webkit.org/changeset/42823