Signature cannot be verified for encrypted mail

[Michael Urspringer]

How to reproduce this issue:

I send the same message to the same recipient, one mail is encrypted and signed, one is only signed.

If I display the mail with Mailvelope, the encrypted mail is successfully decrypted, but there is the message " Signature unknown
Key with ID #2C20D779ED8DE4BA not found.".

The message which has not been encrypted but only signed, however, shows " Signed Michael Urspringer [e-mail] #2C20D779ED8DE4BA".

So it is the same key and Mailvelope seems to know that key, but cannot verify the signature if the mail was encrypted.

Is there anything I do not understand correctly or is this a bug?

P.S. If I decrypt the mail with an external tool like Kleopatra/Gpg4Win the message shows correctly signed.

Update: Could this be the same issue as in #771 as it does correctly verify the signature if I switch to the GnuPG backend instead of OpenPGP.js?