The Product Categories Widget doesn't work in dropdown mode

Hi! I'm using MarketPress and I've added the Product Categories widget to my sidebar. I want it to be a dropdown menu, but when I select that and then try to choose a category - nothing happens. When I unselect Show as Dropdown it works just fine.

I found a number of people having this problem in the forums, but no solutions. Am I missing something?

Thanks,
Wendi