I would like to be able to differentiate between them.

If you are interesting in knowing for sure when the user selected something from the list, use the Valid() method. If this combi is style=2-dropdown list, the valid only fires when the user selects something from the list. If the style is 0-dropdown combo, then it will also fire when the user merely tabs through the control. In this case, you can put this line of code in the GotFocus() of the combo:

This.tag = TRANSFORM( This.Value )

and then you can check to see if the user actually selected something new from the list in the Valid like this:

IF NOT ( This.Tag == TRANSFORM( This.Value ) )
  *** User selected something new from the list
ENDIF