I’ve discovered what I believe is a bug with large rotated screens and separate X screens. I don’t use Xinerama or TwinView. I run 3 Dell 27" 2560x1440 monitors in portrait mode using xrandr rotation.
With driver 295.71 (and earlier), I was able to move my mouse freely between screens. With more recent drivers, I have only been able to move my mouse “right” between screens. The screens are rotated 270. If the screens are not rotated, mouse movement is normal between screens.
With driver 310.19 I’ve noticed a new change. Now I can only move my mouse to the “right” between screens in the top half of the screen. (I’m guessing the top 1440px, but that is just a guess).
I lack the vocabulary to truly explain this issue, but the mouse is now “jailed” from moving to a monitor on the left, and to a monitor on the right from the bottom half of the screen. I’m assuming something is being mis-reported about the screen dimensions and orientations, but have had trouble searching for a solution due to lack of terminology. I’m happy to provide considerably more info.