Created attachment 274995 [details] Test reduction non fractional pixel position.
top:510px does not work either. Apparently when the input box is on tile boundary, outline does not get repainted properly.
That suggests that it's visual overflow rect is too small, or we're failing to take it into account somewhere.
<rdar://problem/25378543>
The fix for this issue was needed outside the WebKit project, therefore this is being resolved as 'Moved'. This should now be fixed in shipping software.