Packages in distributions come and go, but launchpad remembers them forever. The 'linux-linaro' source package does not exist in natty, but the link https://bugs.launchpad.net/ubuntu/+source/linux-linaro/+filebug still works and allows users to file bugs targeted to the default distro series.
It would be keen if Launchpad could prevent filing bugs against packages in series where they don't exist. A URL like https://bugs.launchpad.net/ubuntu/maverick/+source/linux-linaro/+filebug should still work to allow bug reports against *past* releases, but permitting users to file bugs against the default distroseries for packages that don't exist in that distroseries causes busywork for bug triagers. Could LP DWIM please? :)
(Note, linux-linaro is not the only package where I've seen this problem; just the one I have to hand for the current cycle.)
I'm a little surprised this is still an issue, we were cleaning up things in this exact space recently. The mechanism here is that we look for a publication before permitting bugs on sourcepackages...
perhaps we're only looking for 'ever published' not 'currently published'.