Hi,
A number of people has noticed since Outlook 2011 14.4.5 Q4 of 2014, Exchange users can no longer move / delete emails in sent items. When they attempt to move emails it will be copied out instead.
My current Outlook version is 14.4.9.
I was advised to create this post hopefully someone can help.
http://answers.microsoft.com/en-us/mac/forum/macoffice2011-macoutlook/outlook-for-mac-2011-1445-sent-items-sync-issue/4067c85a-bb48-455e-bf84-7d0ae4c20081