OK, so it seems it’s not just a preview issue.
I’d reckon that if your asset duration matched your menu duration, you would not see this problem. You might want to try that as a workaround, if you’re looking for a quick solution.
If you have a little more time to poke around, you might want to try a shorter menu duration – does the same thing happen if its duration is 15 seconds? If not, find out how far you can push it before the problem shows itself.