[AccessD] Question about Listbox Finders on a subform

I have a form with a listbox "finder" on it, generated by the wizard. As
a standalone form it works perfectly: I select a row in the listbox and
it navigates to said row. When I drop this form on a tabbed form, it
ceases to work. I can't figure out why. It may be something obvious, but
it's been a while since I've done Access development and if I ever knew
the answer I've forgotten. 

Any suggestions?

TIA,
Arthur