Yes Nicolas, it's affecting to the people using git flow. I'm using it and it's easy to reproduce the bug.
A strange thing on this is that if you push a branch name called "feature/foo" it will bring a 404. If you do some commits on other branch like 'develop' and push it you will be able to see "feature/foo", see their commits and navigate throw that branch. If you commit then to that branch and push it will come back to the 404. Strange behavior.
Sorry for the lack of progress on this, hopefully we'll get this fixed soon. We always link to the actual hash in the branches dropdown, but the problem exists when you doctor the URL and write the branch name with slash in it. Do I get it right?