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

[PGNet Dev]

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

hm.  'repair' here does nothing for me.


looking at my current TBird settings for disk/cache/offline/subscription,

	browser.cache.check_doc_frequency,              1
	browser.cache.compression_level,              0
	browser.cache.disk.capacity,              0
	browser.cache.disk.enable,              false
	browser.cache.disk.max_entry_size,              51200
	browser.cache.disk.smart_size.enabled,              false
	browser.cache.disk.smart_size.first_run,              false
	browser.cache.disk.smart_size.use_old_max,              true
	browser.cache.disk_cache_ssl,              false
	browser.cache.memory.enable,              false
	browser.cache.memory.max_entry_size,              5120
	browser.cache.offline.capacity,              512000
	browser.cache.offline.enable,              true

	mail.server.default.offline_download,              false
	mail.server.default.autosync_offline_stores,              false
	offline.download.download_messages,              2
	mailnews.offline_sync_mail,              false
	mailnews.offline_sync_news,              false
	mailnews.offline_sync_send_unsent,              false
	mailnews.offline_sync_work_offline,              false
	offline.autoDetect,              false
	offline.send.unsent_messages,              2
	offline.startup_state,              0


	mail.server.default.check_all_folders_for_new,              true
	mail.check_all_imap_folders_for_new,              true
	mail.imap.hide_unused_namespaces,              false
	mail.imap.auto_unsubscribe_from_noselect_folders,              false
	mail.server.default.using_subscription,              false
	mail.imap.hide_unused_namespaces,              false
	mail.server.default.override_namespaces,              true

i _thought_ that^^ should eliminate local caching.

sounds like, perhaps, i've misconfigured, or am missing, something ...