[Users] On shared mailbox, mails sometimes disappear for days

[mat]

Here we share a mailbox on shared storage between multiple logins at the same desktop PC.
After a fix by Paul regarding .claws_cache and .claws_mark files on shared storage, this generally works fine.

However, sometimes we see a mail on the provider's IMAP server (with a different program), and when we get it using Claws, it is not visible there, although it has disappeared at the provider. If we then use a different login, we don't see it either. It will usually appear some days later, and disappear again, up to now we think that eventually it will appear permanently.
Like Monday we retrieved a mail, not seen. Tuesday evening late, is was visible for me. Wednesday morning not visible for the other login, and then not for me either, and Thursday morning neither.
I have done a full file search (using silversearch) on both shared and non-shared storage for unique words which should be in there, to no avail.

What is happening here? Where do those messages hide?

I have noticed that each login has their own .claws-mail/tagsdb/#mh/Mail directories, which directory structure mimicks the one on the shared Mail directory, and which contain .claws-tags files, which seem to be updated. Should this not also be on shared storage? I found no configuration for it.

Also, the .claws-mail folderlist.xml file seems to keep track of how many messages per folder are unread. I do hope these are slaved to the mh_sequences file in the shared storage mail directories.

MatN