Hi Robert, yes unfortunately in 10.9 Mavericks Apple made some major changes to how multiple monitors work, and often times major changes at the operating system level leads to compatibility problems in applications. It seems to be a recurring problem just with the way Apple operates I guess, they often seem to be fiddling with a lot of base level stuff from release to release and breaking various things along the way.

The specific problem is in a component called XQuartz which MoI uses, the problem has been reported to the maintainer of XQuartz who has said several times that a fix will require some further changes at the operating system level, and so this probably won't be fixed until a future operating system update, and then it will take a while for the fix to trickle down into the setup that MoI uses.

In the meantime you should be able to solve the problem by changing the setting to return to previous style multimonitor behavior, that setting is under System Preferences > Mission Control - uncheck "Displays have separate Spaces" there. You will then need to reboot your system in order for this change to take effect.

- Michael