I don't know if this is specific to HipChat, but that's where I've observed this. When using the HipChat integration, we get messages in the chat that look like this when people push to a repo:
The branch mentioned on the first line is the branch of the first commit in the push. That can be pretty misleading if the commits after that went to different branches and just happened to be pushed at the same time. It would be nice to get headings between the commit messages where the branches change.