Ok, I've looked further into this problem and discovered a wierd (but effective) solution.

As the combo array had been re-loaded, I tried the usual 'trick' of re-assigning using this.controlsource=this.controlsource (and the same with rowsource) but this did not solve the problem.

To check that combo.refresh was firing I inserted WAIT WINDOW "Refresh firing" TIMEOUT 2 in the refresh method. The message displayed, but so did the combo's contents!! So I replaced WAIT WINDOW... with INKEY(0.0001) (a very small delay which will not hit performance), and it works every time!

Has anyone any idea what is going on here, and why the small delay 'kicks' the combo into displaying the correct value?

Many thanks,
Alan