kmail sends attachment but deletes message enroute

hi, everybody! i'm using kmail-tde via the protonmail bridge beta for email, and i've encountered a puzzling issue. when i send a message with an attachment, the attachment arrives but the message space is labeled "Empty Message." this is problematic for a number of reasons. of course i first got in touch with the protonmail people, and we went through a few tests -- plain text vs. html and so on -- and no joy. they've pointed out that the only linux client they support, anyway, is thunderbird, so for everything else we're on our own. (i do not like thunderbird and like it even less for its poor support of maildir.) looking in kmail configuration, the lone reference i see for attachments (beside turning on the flag to tell me i used the word "attached" without attaching anything) is some sort of outlook mode, which when checked flings a warning of Very Bad Things if i use it. (fwiw, protonmail bridge does support outlook.) before i check the box, anybody know what's going on with the attachments sending but the messagfs not? btw, they show up just fine in the sent-mail directory. tia. -- dep Sent with ProtonMail Secure Email. Because privacy matters.