[imp] msgcache and shared folder

[Marco]

Hi all,
I have horde-webmail-1.2.4.
I configured IMP with
$conf[msgcache][use_msgcache]=true 
$conf[mlistcache][use_mlistcache]=true
and memcache.
IMP has IMAP backend; server IMAP supports shared folders (rfc2086 enabled and
working).

I notice that with shared folder, if a user changes an IMAP flag on a message
(for instance answering to a mail), that flag modification is not visible by
other users. Even if they relogin to imp, flag message doesn't change.
Only the user that made a flag change see it.

I have to delete manually the cache (memflush) to let flag change appearing to
other shared users.

Did anyone observe this behavior?
Could I have flag working without remove cache?

I thank you very much for every hints.
Regards
Marco