PGP Signed Emails & Formatting

When I compose an email, my default is for HTML.
I often use un-numbered lists to help people more easily consume multi-part processes as I am solving complex problems.
However, after I have turned on PGP signing of my emails, it appears that all formatting and embedded images are being stripped out when it actually gets sent. My clients are not receiving formatted emails.
The only option I have is to deselect the signing of an email if it has formatting at all… which means I need to turn off signing as my default.
Is this the expected behavior?