Well, whaddya know? In the valid of the text box I commented out the manipulation of the combo:

With .cboOperators
* .Requery()
* .Value = This.value
EndWith

In the IRChange() of the combo I included the 2 lines:

This.value = This.List( This.ListIndex, 2)
Thisform.txtOperator.value = This.List( This.ListIndex, 2)

and it works! But this is now quite different from the other pair of controls.

Go figure! The vaguaries of VFP combos have always been a mystery to me.

Thanks, Boris and Marcia for your interest and attention.

I daren't allocate stars to my own message, to indicate it's solved, for fear of that mad Quebecois jumping on my back :-)