We ran into this same problem and going from notes here we hacked a different band aid into the logon script (this is hokey at best and I've got far worse ways to describe this...)
We added a sleep statement at the top of the logon script which delayed the drive mapping, this (so far in testing) appears to work for all of the workstations we tested on. Simply add the timeout command to the top and see what you get. Your experience may vary...
timeout /t 60