Our source vBulletin installation is also using mysqli and
$config['Mysqli']['charset'] = 'utf8';
To continue beta testing we've helped ourselves by adding
$pmText['touserarray'] = iconv("UTF-8", "ISO-8859-1", $pmText['touserarray']);
For some reason the importer seems to handle everything else just fine (posts, threads, forums, etc.)
So I'm not sure why this ugly fix is required there? Does it handle a source database in utf8 that's been using mysqli charset utf8 correctly?
Or is there indeed something wrong with our database that I'm missing?
P.S. this is somewhat already discussed here: http://xenforo.com/community/threads/hung-up-on-importing-pms.4904/
If you want to merge these thread feel free to do so. I just thought I better post a new thread with all these technical details. Hope you don't mind.