When combobox is initialized with a selected index, the first time the dropdown is drawn, it contains only the selected item, like in the following image:
[upload|ZSqaO6MyzFCAe38LECkf4llwV1U=]
When the dropdown is closed and reopened, everything looks fine:
[upload|eTj9R3lm0gQHCev/CALoHa835qA=]
The sample program used to make these screenshots is attached: link text