Deleting remote branches

There is more intuitive

git push --delete origin branch_name

in git for several versions already.

what you're doing is using git's ability to not have a 1 to 1 push requirement.

You can do:

git push origin experimental_branch:master

and that will push your experimental branch to the master branch.

git push origin :master 

is pushing "nothing" to master thereby deleting it.