Sending a mail from a proxy mailbox to a personal group has 0 recipients.

A userA has configured in his PAB a group with few members in. If userA now proxy in a userB mailbox and sends a mail to this group from userA address book, mail is sent fine, however, it is delivered to none of mailboxes defined in the group. There are 0 recipients / mailboxes listed in a properties of sent item. 

This has been reported to our engineering.