Drafts in Mac Mail remain in Drafts Mailbox even after the emails are sent

I'm using MacMail as a client for an IMAP account with Zoho Mail.

Every so often, after sending an email that I may have been drafting for a while, I notice that earlier drafts remain in the drafts mailbox and do not automatically expunge.

When using the Zoho webmail client to send mail, this does not happen - the draft automatically disappears after the final email is sent.

This seems like an error with Mac Mail. Has anyone else encountered it and (if so) do you have suggestions on how to fix. There was a thread on this some years ago at https://discussions.apple.com/thread/8325269 but the issue was not resolved.