I have a problem that vBulletin seems to be automatically reposting new threads in another forum.
The new threads have identical topic titles and show the first 1 or 2 lines of the original forum post with a 'More...' link to the original post.
The new posts are made under my user account.
What could cause this behavior? I have disabled pingbacks. It seems this is some sort of built-in behavior, since it's been an issue since I did maintenance 2 weeks ago. I have however no idea what it is I have done, that could have caused this.
(I will not post links for example purpose, as this might be considered spammy)
Sounds like you have enabled an RSS Feed for your forum?
I suspect that I could re-create your problem by adding the RSS feed for my vBulletin site (eg: http://www.mysite.com/forums/external.php?type=RSS2) to the RSS Feed Manager and have it post new entries as posts in one of my forums.
You don't mention which version of vBulletin, so I'm going to assume v3.8.x (v4.x might be slightly different). Login to your vBulletin admincp, then look for the RSS Feeds > RSS Feed Manager option on the left.
You should be able to disable or remove the feed in question.