Reference to this post but it's quite old http://social.technet.microsoft.com/Forums/windows/en-US/1d114f2b-c00c-47f0-997a-05bf4177ad65/duplicate-mapped-drives
However, I have the same issue on Windows 2012 Server. It is the PDC and there is no Secondary domain. It's primary function is AD and File Server.
The GPO maps the network drives that is common for all users, and then the user login script maps the user's personal drive only. The workstations now keep remounting drives with different letters but it is the same folder location.
For example, a user needs 4 drives to be mapped from the GPO + 1 drive from the login script which is his personal folder.
The 4 drives mapped, will eventually turn to 8. There is no fixed interval when this happens. Also, users effected by this are also complaining that they can't connect a USB anymore. That may be related to this problem, because I haven't set any restrictions in the GPO for mounting USB devices.
Any help would be greatly appreciated.