Solution: imported_ users....
 

I'd like to start by saying i'm truy dissapointed how many times i read up here it is impossible to have duplicate users by officials and how many times there is a reference to merging users. In my case i have 46000 duplicates on a total of 60.000 users so this was not an option. Off course i started a fresh install and no users existed in the DB of vbulletin other than the admin.

We spent all day trying to figure it out and can tell you now we succeeded...

01 - Disable the forum before you import users and posts, forums, threads!!
02 - Start the import from within the control panel and not direct link
03 - Only 31 duplicate users where found in the end instead of 46000

So i guess, importing into an active forum confuses the impex system totally. This was after over 25 trials to import and migrate to other forums for testing as well... I hope this will help a lot of other users as well to get rid of the imported_ prefix problem on users... The few that in the end are having the prefix, are probably duplicates. In my case, it was 31 X true after the import...

Enjoy
Hi-Jack