While cleaning up a certain Hg (Mercurial) repository, I noticed that an old revision (actually 4 years old) shows a branch going nowhere on the default branch.
I thought it wasn't possible to branch the same branch (I mean, you can have a new head on a new branch, but not on the same branch). What is happening here and what did the (then working for me) programmer do here incorrectly, and more importantly, how to prevent it?