A million years ago (in Internet years), Jeff put a tag blacklist in place to stop people tagging things with linux or unix. Probably makes sense but I think his regex was bum:

^linux|unix$

I suspect (though it's been a while since I've meddled with .NET regexes) that it's interpreted as:

begins with linux or ends with unix

Which I don't think was the original intent at all (which was to block the linux and unix tags).

Why is this a problem? Well I've just tried to tag something as linux-headers (a real package in Ubuntu) and a pretty important one if you're compiling stuff against the kernel. Of course there are flowery alternative I could pick (or create), but I just don't see why this is blocked.

TL;DR: I think we need the regex updating to:

^(linux|unix)$