Message attachments, relocated with Tbird in Dovecot maildir store, not openable; reversible by moving BACK to inbox?

[PGNet Dev]

4/1/22
> I see same symptoms when opening a mail in thunderbird 2 or 3 weeks after I received it, without moving it in another folder.
> But using "repair folder" in TB, I get it back, so for me it looks more like a TB cache problem.

I've still not managed to solve for this problem; 'repair' doesn't fix it.

Anyone here have a reliable fix -- either on the TBird &/or Dovecot sides -- to get these subfoldered attachments openable/readable?
Ideally without the need for manual intervention each time?

The issue, again is:

Email with attachments (e.g., pdf) I receive to an account INBOX can be accessed in TBird/Linux with no problems.

Dubl-Click on the attachment, and it opens in app -- e.g. pdfs open in Okular.

Saving the attachment to Desktop,

	ls -al /home/pgnd/Desktop/SomeFile.pdf
		-rw-r--r-- 1 pgnd pgnd 197K May 18 07:49 /home/pgnd/Desktop/SomeFile.pdf

All good.

If I move the message , including attachment, to any other (sub)folder, and try to open the attahment,

I get the usual open dialog,

	You have chose to open:

	SomeFile.pdf
	which is: Portable Document Format (PDF) (66.7 KB)
	from: imap://mx.example.com:993

	What should Thunderbird do with this file?
	[X] Open with 'Okular (default)'

which, on 'OK', does open Okular -- with an Error:

	Error -- Okular
	Could not open file:///tmp/pid-59993/SomeFile.pdf

checking

	ls -altr /tmp/pid-59993/SomeFile.pdf
		-r--------+ 1 pgnd pgnd   27 May 18 07:46 'SomeFile.pdf'

If I move the message BACK to imap INBOX, and open/save attachment it's good again.

Thunderbird is not correctly retrieving the attachment when the message is not in imap:INBOX.