I think it's that rotating the left monitor makes it narrower. So its right edge no longer touches the right monitor. They're not joined in screen space any more as a single region, but two separate regions. And the mouse cursor logic can't/won't warp between multiple regions.
We could go to the trouble of making such a display config impossible, but it's probably more sensible to just ensure the mouse can move freely even in regions not covered by any monitor (to the extent of the bounding box of all monitors at least).
I think it's that rotating the left monitor makes it narrower. So its right edge no longer touches the right monitor. They're not joined in screen space any more as a single region, but two separate regions. And the mouse cursor logic can't/won't warp between multiple regions.
We could go to the trouble of making such a display config impossible, but it's probably more sensible to just ensure the mouse can move freely even in regions not covered by any monitor (to the extent of the bounding box of all monitors at least).