Looks to be a bug in the fullscreen plugin (fullscreen.dll) - everything is a global variable (when the second window went fullscreen it overwrote data about the first). A re-write to store the info for each window to a seperate place is needed.
Looks like we really need a Destroy() pluginFunction (event? :]) to fix this... Or at least stick it into the subclassed window function. I vote for the Destory() since that would mirror Create() nicely.
Can't fix this now, will look at it in a day or two. But then again it's not my dll