Why does Outlook read recent emails when opened?

Question

IMAP

A few weeks ago there was a problem - when opening the Outlook 2013 client, new emails are marked as read. At the same time, not all, but only, for example, 8 out of 10. They sinned about reading when choosing another message, turned on reading only with a double click, the problem did not go away. Mail is connected via Exchange or via imap to the same Exchange Server 2010. On the server, the letter remains unread until you open the mail client. Opened mail through OWA, everything is fine there. As soon as opened the client - mail was read. Changed passwords, reset configs - nothing helped. Scanned with antivirus, found nothing. We do not use POP3 in principle, all clients only through Exchange or IMAP. It is noteworthy that not all users have the problem (about 10 out of 80 machines), but more and more people are starting to show up.