mozilla/kuma — pull request #435 by darkwing (2012-07-23 19:59:22+00:00)
Title: fix bug 774184 - prevent duplicate slug error message

So the issue is that when splitting the slugs, and passing them to the validation routines, only the "specific" slug from the form makes it to the validator, not the entire string; thus "/CSS/length" was getting validated as "length", and that caused conflicts.