Invitations from the iCloud calendar in Zimbra break contacts, where to dig?

Question

Calendar

Dear community. Faced a strange problem.
Installed Zimbra 8.6.0 (post.mycompany.ru) on Ubuntu 12.10. Users connect via imap in Mail.app on Macs.
There is a user Ignat, he uses his personal iCloud, sends an invitation to [email protected], Platon sees a letter:
from "Ignat" to "
[email protected] "
the answer is "2_GEYDMMRRGM2DGO[email protected]imip.me.com>"
Plato accepts this invitation and it is successfully added to the calendar.
After some time, the user Platon raises an op that he allegedly received a letter where "Ignat" is indicated in the to whom field, but in fact the address is indicated "
In Mail.app we go to "previous recipients" and we see entries among others:
Name - Ignat
email - [email protected]
and another such entry
Name - Ignat
email <2_GEYDMMRRGM2DGO[email protected]imip.me.com>;
Exactly the same picture in the Zimbra web interface.
That is, somehow there is such a confusion. Which can cause catastrophic consequences if suddenly a confidential letter goes to Platon instead of Ignat.
I would be grateful for any information.