[Users] Problem with 2 PGP-keys for same address

[Ralf Hutter]

Hi everybody,
i made a new PGP-key, but Claws would only decrypt the e-mails signed
with the old key. When i click on an e-mail that requires the new key,
i get "decryption failed" without the window for the passphrase
opening. I am able to decrypt with the new key when i copy the e-mail
to a terminal and use gpg directly there. 
I obviously want to keep the old key. And on another computer i was able
to use the new one while still having the old one on the keyring, but i
don't remember how i did that.
What is the trick in Claws to be able to use 2 PGP-keys for the same
e-mail address?
Thanks in advance.
Ralf