GetVstoObject method crashes word when Automation Security set to Disable Macros

Question

We have developed a Word VSTO add-in that uses the ApplicationFactory.GetVstoObject(_Document) Method to access specific properties of a document.  When setting HKEY_CURRENT_USER\software\policies\microsoft\office\common\security\automationsecurity to 3 it crashes Word.  We have a large customer who is insiting we fix this issue as their security team need to protect their users by setting this policy.  We use the exact same method in Word 2010 with the same settings and it does not cause any issues so we cannot find any reason why this would be a problem on Office 2013 only.  This is rather urgent as we are at risk of losing this client if we cannot find a resolution.
The add-in loads fine, however it crashes word as soon as the object is created.