Silverlight DomainUpDown can't click on controls

Question

If I define an ItemTemplate for a ListBox, it can contain scrollviewer, hyperlinkbutton, etc. When I highlight an item in the ListBox, those controls work properly.

However, if I use a DomainUpDown, instead of a Listbox, and use the same ItemTemplate, the data is displayed fine, but the mouse clicks are not going through to the scrollviewer or hyperlink controls.

Why not?