[horde] Problem with Horde "Mailbox does not support mod-sequences"

[Luca Bertoncello]

Hi list!

I have a Server with Debian 8 and Dovecot 2.2.13-12 (from Debian  
repositories) and Horde 5.2.13.

When I delete an E-Mail, I always get the error "Mailbox does not  
support mod-sequences".
It results in having the E-Mail not moved to Trash and I must update  
more times the folder to see the E-Mail moved to Trash...

Unfortunately, I couldn't get any help from Dovecot list, so I'm  
trying here, with the hope that someone here use Dovecot, too...

Could someone help me to add this support for mod-sequences?

Thanks a lot!
Luca Bertoncello
(lucabert at lucabert.de)