Probably the documentation should be changed.



First-time administrators (as it was in my case) don't know what a 
"preferences container" is and why they should use it, that's what the 
problem was in my case. I was just not aware of that the sorting is a 
"user preference".



Probably the following sentence should be extended from:



Horde applications can store user preferences in an SQL database, an 
LDAP directory, an IMSP server, a Kolab server, or in PHP sessions.



to:



Horde applications can store user preferences in an SQL database, an 
LDAP directory, an IMSP server, a Kolab server, or in PHP sessions. 
You should configure a preferences container, or unexpected results 
could occur in horde applications.

Because this is not an error. The mailbox sorting works. We won't 
provide non-sense error messages for administrators that don't read 
the installation documentation.

Why not?



If something doesn't work as expected because of a misconfiguration, 
there should be an error message.



Implementing an error message also would reduce bugs and the time 
amount required by the bugbusters to resolve the issue.

No.

Okay, i found out that no preference container was configured. This is 
pretty unintuitive, probably IMP should throw an error (to 
administrators only) if preferences cannot be stored?

When i sort my inbox using the buttons (e.g. 
http://server/horde/imp/mailbox.php?sortdir=1&sortby=1&actionID=change_sort), 
it works until i reopen the folder or use the paging buttons.



IMP should remember the sort order at least globally (and across 
paging), nice to have would be a folder-dependant sort order 
remembering.