Kris, did I misunderstand your problem. when Iread your original post I thought that the script you used and the methodology of using the groups had your script attempt to map the same share name more than one time. If this is a scripting issue my suggestion would eliminate the the duplicate attempts to map the same drive.
If you problem is not that you code is making multiple attempts to map the same drive, and it is in fact that multiple drives appear to be mapped to the same server\share location that is not a result of your script, then you issue in not your script. Please clarify which problem you are experiencing.
Include writing a logfile of all mapping activity in your script, how does that compare with the drives currnely mapped after the logon script has finished? Are the extra drives always to the same location?