See:
http://answers.microsoft.com/en-us/onedrive/forum/odwork-odfiles/multiple-document-folders-appearing-under-this-pc/caebd146-1f30-4ff7-a1ab-0301ba557438
Workaround
Remove the "Documents" from "This PC" using the following
link.
Direct download link for
Remove-Folders-From-This-PC-on-Windows-10.zip.
I also unpinned it from the Quick access (rightclick and choose "unpin from Quick access").
Now I have "Quick access", "MsOneDrive", "This PC", "Network" and "Homegroup", all behaving quietly. Since "MsOneDrive" is mentioned as a "root" element in Explorer and contains "My Documents", it was no longer needed to have them in "This PC" or "Quick access".