Hi dethegeek,
it's really great that you are thinking about my problem even though it is already some days (or weeks?) ago that I posted it.
I cannot check anymore if usernames are identical in both fields you mentioned because I have already renamed the user "fafnir" some time ago, and I really don't remember if there was a difference between both fields in the user properties of AD. Maybe that in one of the fields the username was written with a capital "F" and in the other one not, but I don't know for sure, but if there was a difference, then it was a really small one like capital letters or not.
I tried to access to the personal folder of the renamed user "fafnir" (which is now named "hans"), which has been newly created on OMV, and what should I tell you? It works. This evening I will try to rename the user back to "fafnir" and check the accessability of his personal folder (I will delete the old one at first).
I will post it later. Thank's again for your persistance.