I noticed some behavior I didn't remember seeing before on a 1.5.21 build recently -- when I did a body search in my sent-mail folder, mutt automatically tried to decrypt every single pgp-encrypted mail in my sent folder (and, since I don't use gpg-agent, seemed to request my passphrase for each one, though normally mutt doesn't require me to enter it more than once within a short period of time).
Is this normal behavior, and is there a way to avoid it (a quick search for the crypt_* stuff in TFM did not bring up anything obvious for me). w