Cannot switch repository from private to public

The "This is a private repository" checkbox is disabled, and even if I enable it using "Firebug" and submit the form, the value still does not get saved.
This happens on a repository that I own (not a fork) and I was able to switch it from private to public before.
For info, I'm running Chrome 60.0.3112.101 on Windows 10, 64bit.