onPress ComboBox Conflict

I have a symbol behaving as a button that uses the onPress event to increase a counter that’s displayed on a label. Repeated clicking on the button behaves as expected untill a combobox on the same movie clip has been activated, at which point repeated clicking increases the count only sporadically unless the mouse pointer is moved between each click. Here’s a sample of the onPress ComboBox Conflict, the fla is also available there.

Can any one shed some light on why this is happening and even better how to resolve it?