I have the same problem with Elder Scrolls IV:Oblivion. I have the same version on both machines as the original poster. I use the option to only changes screens if the shift key is held down. That is the only non-standard option I use by the way. I can hold down the shift key and mouse over from my gaming (primary) machine to my surfing (secondary) machine to look at an Oblivion walkthrough or forum or whatever, but then when I'm done, I cannot get back over to my gaming machine. My gaming machine must be restarted completely to gain control again. It is mindbendingly frustrating, having just read about what to do next in a game when you're stuck, to not be able to mouse back over and actually do it!
This was one of the main reasons that I bought the app - the ability to play a game and get game reference info on the fly at the same time, without taking my hands off the mouse and keyboard. Not only does it not work, but attempting to use it in this way is malicious in effect.
What say you Neil? Buying Multiplicity also led to my subscription to Object Desktop and various other shiny things purchased, which in total cost much more than a copy of GCII!!
Can we at least get an update on v1.1 progress and the enhancements/fixes being worked on? GCII honeymoon is OVER!