> That arrangement had been working for me Well, it has not been working for me. And I've tried rearranging the displays. I'm not stupid. I had a similar setup

> That arrangement had been working for me Well, it has not been working for me. And I've tried rearranging the displays. I'm not stupid. I had a similar setup with a single Mac before, and it worked fine. The layout looks correct in System preferences. When moving the mouse between A2 and B, the cursor comes out in the right position. I just can't move from B to A1. (A detail I omitted for brevity: I can move the mouse from A1 to B, but then the cursor jumps down as if it was coming from A2.) It's definitely a bug, it's not intentional.