Comment 6 for bug 1827369

I've at least added a message to the "Change your OpenPGP keys" page now, noting the limitation and linking to this bug.

Unfortunately it seems likely that we'll need to do some infrastructure upgrades before it's possible to fix this bug. The new bindings in the python3-gpg package are much better in my experience, but I don't know of a reasonable way to get those working on xenial (and we definitely want to stop running on xenial as soon as we can find time for the upgrade).