Moving a group email to a personal folder

[aktary]

Here is the problem we're having:

- User A receives an email in the group folder, support@company.com.
- User A right clicks the email, selects "Assign to", and assigns it to User B
- User B receives the email in her "My Email" folder.
- User B moves the email from her "My Email" folder to a personal sub-folder so she can work on it.
- A COPY OF THE EMAIL MAGICALLY REAPPEARS IN THE GROUP FOLDER!
- If User B moves the email back to "My Email" the copy in the group folder disappears again.
- If she then moves it again from "My Email" to her sub-folder, the copy does NOT show up again in the group folder.

How do we fix this?

I simply want the email to follow one path, not have mysterious copies showing up and disappearing!

[edit] I forgot to mention, we're on Version 5.2.0d (Build 5604) Community Edition [/edit]