attachment menu is prompting when it doesn't need to for S/MIME

I've an email with an attached signed p7m file. Upon viewing the email I get the notification that S/MIME signature successfully verified. When hitting v to view the attachments list (a few attachments) I get prompted: Enter S/MIME passphrase:

I've no idea what the prompt is expecting me to type in, so I hit enter and I get prompted in a different way: Enter keyID for strk@kbt.io:

Failing to know what to type in there I try ENTER but isn't enough to get past that prompt. Hitting ^g gets over it and shows me a list of the attached files but the p7m one is missing.

This is with Mutt 1.9.4 (2018-02-28)

I was asked by @kevin8t8 to report this here