is the ComboBox behaving correctly when selecting an item in the dropdownlist?
currently, the dropdownlist collapses as soon as the mousebutton is down to select an item, not when the mousebutton is released.

I revised the behaviour in WPF of ComboBox, Menu, and ContextMenu controls and you are right. The correct behaviour is to wait until mouse up for selecting an item.

We take note and will change it in a future release, thanks for reporting.