I tried it again. I dropped a SCREWTERMINAL-3.5MM-4 onto my board, with the schematic window closed. It allowed me to position it in the + quadrant. When I used the button on the board window to open the schematic, I don't get any error messages.
On the other hand, I don't see anything in the schematic that wasn't there before.
Maybe someone else knows how to make this work properly.