In the Flex SDK 3.5.0.12683 the ComboBox Class has a strange behavior, if you change the dataprovider after you have played with your ComboBox, the list of item in the dropdown is not refreshed.
Possible solutions to the problem are :
1) Switch back to the 3.4 SDK
2) Add the following few lines of code after updating the dataprovider : myComboBox.dropdown.dataProvider = yourArray;
Enjoy : )