Duplicate Emails in Outlook Sent Items with PGP enable.

I have a user who, with PGP Desktop services enable, has duplicate sent emails in his SENT ITEMS fodler in Outlook. It does not matter if the emails are encrypted or not, every sent email is duplicated. The recipients are not actually recieving duplicate emails. When PGP services are off, this issue does not occur. 

They are using Outlook 2010 with Exchange and PGP version 10.1.0.

There are multiple users having the same setup that do not have this problem. 

Can someone show me how to disable this?