iPhone & Zimbra contacts sync problems

[af465]

I have configured my iPhone to synchronize mail, calendar & contacts to a ZCS server Open Source Edition. The Calendar and Email looks to work fine, but the Contacts have a strange behaviour.

The symptoms are:
- When iPhone established the connection to ZCS for the first time, all the zimbra contatcts were imported correctly.
- If i change or create a new contact on zimbra desktop, the changes will not be reflect on iPhone
- If i change a contact on iPhone the changes will not be reflected on Zimbra server.
- If i create a new contact on iPhone it will appear on Zimbra server, but future changes will no be reflected.

On iPhone configuration, Fectch New Data > Push is set to ON. I have tried both Manual and Periodic Fetch, but the behaviour is the same.

Have any one an hint about what the problem can be?
Appreciate any help
Antonio

I access ZCS trough a a Cardav account
Have a iPhone 4 version 4.3.5 (8L1)
and ZCS server elease 7.1.2_GA_3268.UBUNTU10_64 UBUNTU10_64 FOSS edition.