It has been explained before. It happens when a Mod deletes a post, it isn't fully deleted, just invisible to the public. So you get the ghost page.
The true explanation is 'whoever wrote this message board software wasn't thinking'. Someone give me the code and I'll fix it in an hour.
And no, I am not saying 'give me access to the Paradox server', but rather the code in question (I dunno if Paradox have heavily modified their vBulletin system).
Edit: In my own amusement, I thought; perhaps I could just obtain the code myself and fix it, since it is written in PHP. Anyway, it turns out companies are still terrible at handling code and changelogs available for all to read. I'd rather read an open source project's code and changelog than this crap.
Seriously, when I realised I had to wallet up $195 for a vBulletin licence, I thought I either pirate it or
better yet! I read their changelogs since 4.0.4 (since that is what these forums are running) to see if the change has been made.
I even found a thread for
4.0.5 on their official forums (and other versions down the line), but the post itself was limited in content and not a true changelog you would expect from such a public code.
Fortunately!, they had a
full list of fixed bugs. Well, it was fortunate until it turns out they should have installed Bugzilla instead. Gee.
This basically killed my dreams of attempting to find whether 'ghost pages' had been fixed down the line; because let's be honest,
it is a bug and moreover, it tends to ruin a lot of threads on these forums, and I am certain a quick fix (trust me, I develop for the MediaWiki project) would be appreciated by whoever runs these forums, so we can get back on track in most threads.
But I feel dirty pirating the software just for that, I dunno. I mean, I wouldn't use vBulletin myself, I'd probably just use Mailman and do it the old fashion way.