on a system with multiple monitors using the desktop cube effect creates one cube the size of both monitors and places that in the center between those two monitors, so that only a half cube is visible on each monitor. visually it would look much better imho if every monitor had it's own cube centered (any manipulation by the user i would expect to be applied to all cubes identically). windows that span multiple cubes: i would just cut them at the cube edges Reproducible: Always I'm using an nvidia GPU, with the proprietary driver, IIRC that one does multi screen differently - would be awesome if it worked flawlessly on nvidia =)
we had that in 4.2 - that is the initial implementation of Cube. It was a mess - both from usage and code complexity. Sorry will not add that again.