same backup problem

We heard back from development today on this case. In summary, this issue isn't going to be resolved because it is a limitation involving integration into the Windows OS.

Here's why:
The Windows integration element in Backup & Sync relies on some information being stored in the Windows user settings. If you are using the same Backup & Sync account in two different Windows user accounts, that user data has to be replaced between those two users profiles every time you switch over. Otherwise, the integration would not work. Changing this would require fundamentally changing the way the program interacts with Windows. It is actually an unusual use case that the same Backup & Sync account would be in use under two different Windows profiles on the same computer, which is why this is the only report of the issue we have. The only workaround would be to use a different Backup & Sync account under your other Windows login. Basically, it's doing this because that's how Windows has to store its portion of the data, and that necessitates the reinstallation in this odd circumstance. I hope the explanation is helpful.