If I create a new element with a -webkit-box-shadow css declaration, the shadow isn't drawn until the element behind them is redrawn (eg by resizing that element, or the entire window)
Try going to the link above, and create a few boxes. None of the new ones should have drop shadows. Resize the window, and watch the shadows pop into place.
Resizing the boxes doesn't cause the shadow to be drawn, but resizing the element that the shadow appears on (in this case, the page body) does.
*** This bug has been marked as a duplicate of 12729 ***