I seemed to have fixed this by renaming one specific field. It was the first entry in the first custom field. Selecting that and searching seems to have broken the search. But now it returns no result as expected.
I don’t know which plugin was at fault there but it seems to be working correctly at this stage.
It seems the update isn’t being distributed, at least to my wordpress installations. I’m usually quick on updating so would have done that first.
I’ll download it directly from the buddydev website and install it that way.
Thanks for letting me know.