Mission Editor: Object list doesn't refresh

I was trying to move some objects in my mission file into SimGroups and I noticed some strange behaviour. After using the "Add Selection to Instant Group" option, the object seemed duplicated. It appear in the group as well as in its original location. At first I thought the object was duplicated, but when I shut down and re-opened the Mission Editor, everything was displaying correctly. Looks like this is just an issue with the Mission Editor not refreshing properly.

I went back and tried this out on TGE 1.4 and had the same problem.