Be careful working with your Model Groups. A user alerted me that they weren't working right and one of his models got deleted. I found that when we added sorting to the list boxes we weren't keeping track of the selected item properly when adding items to the list so it can cause you to overwrite the wrong group if you hit Update Model. After you hit Add Model you need to select the New Model name up in the list or it can overwrite an existing model at the bottom of the list.
The fix is checked in and will be in 4.0.19.