Cross-premises Calendar Sharing not woking in Hybrid Exchange 2003 - Office 365

Hello there,

Here is my environment: 

Exchange 2003 on-premises 

Exchange 2010 on-premises with Full Hybrid Configuration (no mailbox inside this server): CAS+HUB+MBX Role installed

Exchange Online (new Exchange 2013 wave).

ADFS Farm + Proxy

DirSync with password replication disabled

Most clients are Outlook 2007 

We have most mailbox on premises and moving mailboxes to Office 365.

The following is working: mail flow in all directions, free/busy cross-premises, message tracking. 

I'm having problems with Calendar Sharing.

User1 and User2 are both in Exchange 2003 

User1 accesses User2's calendar in readonly

User2 accesses User1's calendar in readonly

After moving User1 to Office 365 with "Remote Move" either with EMC 2010 or Online-EAC both users cannot access to each other's calendar. 

User1 cannot access Calendar of User2

User2 cannot access Calendar of User1

Any hint?