Rated 4 out of 5 stars

When I toggle encryption and signing off inside the compose message window and save the mail as draft, it's always encrypted.
Because I can't find an option for this behavior I guess it's a bug.

Edit:

thank you for the reply - this settings must have been added some time ago and I just didn't see it since then ...

This review is for a previous version of the add-on (1.9.1). 

That's a feature, not a bug. You can turn off encryption of drafts in the account settings under OpenPGP Settings.