In some other forums which have most recent activity threads on top, people try to keep their favorite threads active by posting meaningless "bump" posts from time to time.
This is usually done on threads where someone asks a question and is annoyed that there is no reply after a coupl of days.
Also happens when one of those "your favorite..." lists with 100 posts comes along, or when a date-oriented post like "2 months until Top Hell Iron Kitchen premieres!!!".
Moderators, I wish you the best with bump removal, hopefully if you remove them the software will reset the thread to where it should be.