Recently i have seen few posts merged together (maybe by the mods).
[moderator's note: consecutive posts merged]
It is not new but in history, rules to merge topics, threads, posts have been changed many times.
(Moderators no longer have the ability to merge topics due to incidents like this.)
Only admins can merge threads, and it's only done for technical reasons such as an accidentally-split post. Merging similar threads together just makes a big mess; if too many topics about the same thing are posted, the extras should just be locked or deleted.
When merging, you merge from a topic into another topic. You don't add two topics and get a new topic. So it'll be whatever the destination topic is. When splitting, the new topic is not self-moderated. If you move a topic to a section where topics cannot be self-moderated, it loses its self-moderated status for as long as it is in such a section.
Split example
Theymos split the thread and the split off part was moved to Archive. Not sure why it went to Archive, as it's more suited for the Trashcan, but whatever. I asked for this as the last 284 were pointless and no longer relevant (and thus spam).