EWS : Appointments : Is there any way to avoid copying the extended properties when copying appointments in the calendar (using ctrl + v) ?

Hello there ... 
I am using the extended properties to store a GUID which is used to identify appointments, since item.ID is changable with changing the folder. 

My problem happens when copying the appointment using the keyboard and when inviting people for a meeting (which I believe all it does is also copying the original calendar item (appointment) from the meeting organizer) it copies also the extended properties (including the guid) . 

So is there any suggestion how to solve this problem ? is there any way to copy items without copying their extended properties? 

Ahmad