Draft encryption is on (with the key for the mailaddress account in use).

Start to write a reply to an encrypted email (in preview).
Switch to another mail.
Go back to your draft encryption after the cache expired.
Cancel decryption (this could be because of timeout, too).
Switch to another mail and back.
When you switch back to the draft encryption after that and enter the password, the body of the mail still displays the "decryption canceled" info box. (The box flickers for a moment after entering the password.)

Markus: I could not (yet) reproduce the case where I managed to get the text of the draft back after editing something in the HTML info Box. In that case I was asked whether I want to save the changes and answered "no". But I did not yet manage to get that question again. Maybe it is related to the configuration setup I had before, where the key for draft encryption was different from the one of the key for the mailaddress.