Alright, I just checked again (I've had it disabled since it stopped working post-patch 2.3) and it now appears to be working for me. Must've been some compatibility issue with with some other addon I had at the time patch 2.3 came around.
I apologize for calling attention to something that there was no problem with.
While we're here and talking about ChatMultiWindows though, I do wonder if it's possibly to add some features to it. Specifically, the option to lock any additional windows you create in place, and placing the chat windows behind trade windows.