Why are you relocating My Documents folder at all? Why don't just create e.g. DOCUMENTS folder in non-system drive and include it in the Documents Library for every user?
I found this out the hardway, but with the inability for my created workspaces to be saved. As it turned out, Premiere apparently puts the preference files where it thinks MY DOCUMENTS was pointing to. If you re-direct MY DOCUMENTS to another drive (e.g., a NAS, as I did), Premiere still writes to to /users/documents..... When I reversed the re-direction the problem went away. As Fuzzy does, I created a "MYDOCS" folder on the NAS, and then mapped that location on each desktop as a network folder so that it shows up in the windows explorer tree.
Thank you for confirming my suspicion that leaving system files alone is the way forward. I tried a multi-disc configuration for video editing recommended by a forum member. Luckily, I experimented on a new computer with the user account. It was easy to restore. The lesson learned was not to interfere with system folders that are used by serious applications that point to system files. A separate documents folder not related to the system is the solution.
My new computer is a 6-core that was custom built for dedicated video editing. Large volumes of document files will not be needed.