Comment 6 for bug 1426171

calibre bundles a modified version of cherrypy that fixes this bug. Try running the recommended calibre binary install from the website. ;)

Ubuntu could fix this problem if it can get calibre's cherrypy changes upstreamed.

Obviously, that won't fix the problem of Ubuntu shipping ancient versions of calibre, but I suppose that isn't a Ubuntu priority.

Aside: See the calibre manual for reverse-proxying calibre-server behind apache: http://manual.calibre-ebook.com/server.html
Then use apache's auth setup, which is much better e.g. HTTPS