movies with transparent backgrounds don't display in KN4

In KN4, movies with transparent backgrounds (such as the countdown timers sold by KeynoteUser.com) no longer display when the show is presented. They clearly function when creating the slide, but not during presentation. I'm running the show on a MacBook Core Duo with 10.4.10 and GMA 950 graphics chips with 64 MB VRAM. This might be an issue with the GMA graphics chip although the movies worked perfectly with KN3 and earlier. Has anyone else observed this problem?