The reason I brought up Symantec is most of my customers have Symantec Corp Ed on their pcs. One of them has been experiencing the same thing you are describing, but it never causes any issues, so we just let it be. However, one of my other customers had a similar problem, except we could not remove the mapped drive, nor could we re-add it. It was like it was deleted, but still existed. Anyway, it turns out it was a bad install of SAV. Once we removed SAV, we were able to remap the drive, and then reinstalled SAV and everything worked properly again.