Paul.
Well, well. Thank you. You nailed it.
My failing was that I did not consider that when one clicks on a menu-style button, a "mouseDown" message is sent before a "menuPick" message. And the mouseDown handler in the card script exits if the target is not one of two particular fields. The button is, er, not one of those two fields. And this was a modification I added while installing a new feature to the stack.
Dangerous business, that, obviously. Anyway, at least I had a backup
Again, thanks, mystery solved, and I learned I have to be a better detective.
Craig
EDIT, assuming I get that new feature installed without crashing my computer, anyone who plays Scrabble is welcome to have that stack. it mostly works.

If even one person asks, I will post the new working stack.