What I do is set the CBO to Alias, rather than field, I don't know it is a bug, or not, the same error generated if it is rowsourcetype=6

it is only one time thing, you don't need to add it to your tables... however, in case you need to add them, I will do it in LostFocus()

IF this.listindex = 0 OR !EMPTY(this.displayvalue)
   cValue = alltrim(this.displayvalue)
   this.value = cValue
   LOCATE FOR cField = cValue in tableA
   IF !FOUND()
      INSERT tableA () Values ()
   ENDIF
ENDIF

That's what I do in a form/grid
Check it out