From https://bugs.webkit.org/show_bug.cgi?id=14344#c13 2) If an element’s position change affects the cursor because it moves under the cursor our moves out from under the cursor the cursor won’t change until the mouse moves. 3) Hover effects also don’t change in cases like (2).
Bug 53340 is about the same issue with cursor shape. Hyatt has suggested fixing both bugs at the same time.