Good point - about is it a VFP base class ? No. I tested it after your reply with VFP base classes and everything works fine. Two things I should have mentioned.
1) I am using a version 'CodeBook' with their ebizobj and ebizobjform classes.
2) I found the combobox does not go blank if you pick the first selection in the combobox. It goes blank on any other selection.
I hope to find time today to more thoroughly debug this since it seems to have something to do with our 'codebook' framework.
Thanks for the feedback to get me to the next step.