Problems with murder upgrade from 2.2.13 to 2.5.8

[Jean Charles Delépine]

Hello,

I'm on the way to make a big (late) upgrade. 

My murder config is composed of 16 1To backends. I can't upgrade 
all of them simultaneously. So I planed to :

  - upgrade mupdate server (make a new one, and update frontend's and 
    backend's conf)
  - replace frontends with upgraded one's
  - upgrade backends one after the other, nightly, on serveral night

mupdate server upgrade is ok. But I have problems with 2.5 frontends and 2.2
backends interaction. All seems fine (no error), but users can't create new sub 
mailboxes (admin can create mailboxes and sub mailboxes) :

loggued as mailbox owner :
imap-01> lam INBOX
delepine lrswipcda
anyone p
imap-01> cm INBOX.hop
createmailbox: Permission denied

My tests say that, whichever mupdate server version :
  Frontend 2.2 can create 2.2 mailboxes and 2.5 mailboxes
  Frontend 2.5 can't create 2.2 mailboxes but can create 2.5 mailboxes

All others tested features work.

The 2.2 is using saslauthd + pam_ldap for authentification. The 2.5 is using either
ldapdb or saslauthd + ptoader and ldap.

With or without 
  suppress_capabilities: ESEARCH QRESYNC XLIST LIST-EXTENDED WITHIN
on 2.5 frontends.

2 questions :
  - do you have an idea why users can't create submailboxes on 2.2
    backends with 2.5 frontends ? Is there any acl new option I 
    miss ? ...
  - what are the risks if I wait for all backends to migrate before
    using 2.5 frontends ? My option with this problem. I didn't find
    any problem... but surely, if there's one, my users will find it.

Options that might be relevant :
On backends :
  proxyservers: proxy
  proxy_authname: proxy

On frontends:
  proxy_authname: proxy
  proxy_password: <>
  proxyd_allow_status_referral: 0
  proxyd_disable_mailbox_referrals: 1

backends are in an internal non routable network.

Sincerly,
      Jean Charles Delépine