I have seen the enemy, and the enemy is me (as usual). Your tip on the "persistent" flag led me down a path to the solution.

The problem with the disconnect was that I had done a 'chdir' into the share after mounting it. And, since I was still sitting in the directory when I went to unmount it, it wouldn't release the mapping to the drive. As always thank you everyone for your input, I have learned much today that I will use again tomorrow!