Attachments not rendered, lost upon saving draft

Version 5.007 on Android 5.0.2:

Some types of message content cause existing message attachments to not be rendered while editing messages. If edits are saved, attachments are permanently lost.

From another client

1. Open Thunderbird* and launch Help > Troubleshooting Information, then choose 'Copy text to clipboard'.
2. Paste into draft message.
3. Add file attachment.
4. Save in drafts.

*It's not clear exactly what HTML content causes this error. Basic entities like bold, tables, & text coloring don't trigger it but the Thunderbird troubleshooting dump does so consistently.

From K9 mail

1. Locate saved message in Drafts folder view
2. Observe paperclip icon on draft, indicating an attachment
3. Open message to resume editing
4. Observe message apparently has no attachments
5. Save as draft
6. Observe paperclip icon is now missing, indicating attachment was lost outright

It's probably worth noting that all HTML is stripped out of the message body when you resume editing with K9 mail.