Try the following steps (taken from TID10053566):
1. Move all message from the shared folder to a temporary holding folder
2. Highlight the shared folder, hit the delete key and select "Items only" (NOTE: upon hitting the delete key, the information dialog that came up, indicated that there was one item in the folder. This item (or ghost item) was not visible.) The user selected to delte "Items only" and the envelope went away.
3. The user then dragged the origional un-opened items back into the shared folder.
Hope this helps!
Alain