Comment 47 for bug 303140

@wroot, if you more carefully read my post of 2016-06-28 01:49:32 PDT you will see that my workaround does not only prevent an error message, but also does enable removing attachments.

I also indicated a sloppiness in TB's way of detecting that a message is signed (when determining whether it allows to remove attachments).

The whole issue could have been solved pretty easily already some ten years ago, but like with most other reported bugs/problems, nobody actually takes it up.