We have the same issue in EWS 5.6 patch3.
Check this out:
There exists a KB for this issue: https://kc.mcafee.com/corporate/index?page=content&id=KB75047
I strongly suggest opening a support case with McAfee, mentioning this KB.
On the support case we have opened, we were told PAtch2 for MEG7 (out in august) would solve this problem.