Dropdown will not disappear after select item

Hi guys,

I have a small problem today. I have a repeater with a submashup which shows a dropdown:

If I click on a item of this dropdown, the item will selected (and shown up as the selected) but the dropdown will not disappears. It stays open. Its only a optical issus but it is annoying if you have many selections.

I'm not quite sure but I thing this have something todo with the repeater. It there any workaround known to fix this problem?