The problem was likely that gpg2 made a /copy/ of your gpg(1) keyring when it first ran. After that they were out of sync.
gpg2 really just needs a gpg1 comparability shim that's good enough that it /replaces/ the gpg1 tools on a system and seamlessly gets them to use the gpg2 keyring.
Before the upgrade gpg2 was able to read the keys just fine.
Now, that's not the only problem after the upgrade, Enigmail is having some other issues...
It's a mess.