Compare-View is broken when branch name contains slash ("/")

My branches are named like "feature/[featurename]" or "bugfix/[bugfixname]" but when I compare such a branch by pressing the "Compare" button, Gitlab returns 404. The URL is

http://gitlab/[group]/[project]/compare/master...bugfix%2Fbugfixname

When I change the URL to

http://gitlab/[group]/[project]/compare/master...bugfix/bugfixname

it works.