mail quoting a gpg-signed mail produces "submit request failure"

[Martin Pool]

I replied, from my Android phone, to a bug mail from John. John's mail was signed, though it might be affected by bug 612754.

Launchpad then replied to _my_ mail to say "submit request failure", I guess because it didn't like the signature.

istm the mime structure here ought to be enough to let Launchpad tell I didn't actually try to sign this mail, though email being what it is perhaps this is always going to be messy. It's a bit annoying that my mail didn't get through at all.