Try REQUERYing the combobox directly:

Forms!Proposals.fkClientID.Requery

(Assuming the newly added item is not appearing in the combo box)

Forms!Proposals.Requery   should work  too, but that would be doing more work than you need to (requerying the...

I get this occasionally in just one subform in A97.  Compacting normally corrects it to showing only related records again.