When using named branches, a target repository will refuse being pushed to if it is to receive a new branch, even when that branch has already been merged again and that merge is being pushed as well. For this situation we have the
hg push --new-branch
option. Using it will allow pushing newly created branches but will still lead to refusal if something else seems fishy. This is much safer than just using
hg push --force
which will enforce things on the target repository that should have been sorted out locally most of the time.
I hereby humbly request a "Push New Branch" checkbox next to the "Force Push" one.