Sometime ago I've deleted a forum with some content inside. I thought that it is totally deleted but today I've created a new forum and found all the content of my deleted one. When I look at the ID of the forum I recognized that they booth haved the same ID. I think if I delete a Forum it just deletes the ID and not the content. This should be fixed in my view.
As I said I've deleted a forum with ID 19 and some content.
The content located in this forum was created by the feed poster.
Structure: Forum home-> category-> forum-> forum (ID: 19)
XenForo version 1.0.1
Today I've created a new forum, it has the ID 19 again and all the content of the forum I've deleted before.
Structure: Forum home-> category-> forum (ID: 19)
XenForo version 1.0.2
The rest of Jake's post is correct, but there is a situation when IDs are reused. If the record with the highest ID is deleted and the MySQL server is then restarted, the highest ID will be reused. (If it's not the highest ID and the server wasn't restarted, it shouldn't happen.)