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#11
I have never seen this issue.
After I install an OS I set WMP as the default player.
Then I install VLC at all defaults which seems to only open those files that WMP cannot play.
Then I install QuickTime which opens only its files such as .mov which will play sideways if not played by QT.
I have never had these change on me, but if they did I would in Control Panel>Defaults set VLC as Default, and then for Apple movies and pictures manually set QT under file associations there.
Any variance from this on a different drive letter where the User folder has been moved would seem to me to be corruption and not having at all to do with the function of moving User folders which I have done for years with no issues whatsoever.
You can read here how I root my User folders in Skydrive to Sync, Backup and Store your Files to the Cloud with OneDrive .
What I would do is reset an affected User folder to default to see how it changes, then move it back again.