Using WebKit nightlies r38068. Open the attached testcase and hover over the outlined box. The boxes rotate, but leave behind cruft and are rendered incorrectly when they get to their rotated state.
Created attachment 24919 [details]
testcase showing bug
Here's another test case which is similar to the reported bug:
Artifacts can be seen in the reflection after a 10 degree rotation. These artifacts appear in all cases except when not rotated.
The first testcase mostly works, but there are still some jaggies left around.
The second testcase is a separate issue; please file another bug.
Created attachment 25826 [details]
Patch, testcase, changelog
r39078 = c7cac524ee5576a4ce13f247ec857214e20cbde5 (trunk)