2.4.17 --> 2.5.3 Some mail folders no longer accessible

[Patrick Goetz]

Upgrading from 2.4.17 to 2.5.3 resulted in one very strange problem. 
Some of the users have a large number of nested mail folders.  After the 
upgrade, exactly one user found that some of his folders (say 3 out of 
30) are now inaccessible.  In Thunderbird they show up, but are greyed 
out.  If you try to subscribe to the folder, the subscribe checkbox is 
missing.  In roundcube they aren't visible at all.

This is pretty clearly a permissions problem of some kind.  The question 
is how could this happen and what's the least painless way of going 
about resetting the permissions so that he has access to these folders 
again?

We're not doing anything fancy; for example, there are no shared 
folders; independent email addresses are configured for shared mail 
content and configured in the MUA.  The problem folders are in an 
unshared account.

Also, the manifestation of the permissions problem isn't consistent 
across the affected folders.  As reported by the user:

Archives Staff:  grayed out, cannot see email
Archives Staff Retreat:  not grayed out, cannot see email, when you 
click on it, it says the action cannot be completed because the account 
does not exist
General Convention Office:  not grayed out, can see email, when you 
click on it, it says the action cannot be completed because the account 
does not exist.

Thanks.