It about 99.99% works, one behavior that is still off is if I have Window
Snapping enabled in Mate Tweak (I normally don't so this particular bug does not cause me any problems), when it's in a corner a Mate terminal only expands to have the screen horizontally but full screen vertically.
Hm, this doesn't sound like a bug. A window is only maximized both vertically and horizontally, if you move it to the top edge. Moving it to either the left or right edges maximizes a window vertically, but only half-way horizontally (depending on what edge you moved it to).
MATE always behaved like that and it's consistent with, i.e., the way Windows is maximizing windows when moving to edges.
Disabling rrxinerama is only a workaround, though. It will break client-side Xinerama setups and maybe other stuff, too. The nice part is that without rrxinerama, the fallback (read: old) code is being used.
Mihai