Now I'm sure that its a BUG in mx:ComboBox(Mac OS X Lion, InDesign CS5.5) as I'm able to reproduce in Adobe's Kuler panel also as follows,
- Open Kuler panel and switch to Browse tab.
- Then switch application(Cmd+Tab) and come back to InDesign.
- Then click on any combo-box(Highest Rated or All Time).
We see that the combo-box is not opened for the first time.
Any help/suggestion/workaround is highly appreciated.