probably it is an issue in ags flex api. So I need some workaround to fix it.
So if I put ComboBox or DropDownList on InfoWindow it will be impossible to close it clicking on arrow button or outside of dropdown and that is not correct behavior for this type of Flex controls.
I assume you are using a custom infoWindow (since you place comboBox and/or dropDownList inside the infoWindow). I did a test and didn't observe the problem that you mentioned here. The only problem I found was that background was transparent.
I have same problem. All dropdowns in edit attribute forms cannot be closed unless an item is clicked. I fact if a dropdown is open and you close the attribute editor widget, footprint of the dropdown still remains in screen!