Outlook appointment item loses extended property when using "shared calendar improvements"

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I'm working on a Outlook VSTO Add-in which is used to create appointments which are linked to third party software. The linking is done by using extended properties.

I just encountered a problem when the option "Turn on shared calendar improvements" is activated. During the synchronisation to Exchange 365 the created appointment loses its extended properties. The properties are definitely added to the appointment and are removed a few seconds later without any user interaction.

The properties are added via Microsoft.Office.Interop.Outlook.PropertyAccessor.SetProperty() using following prefix "http://schemas.microsoft.com/mapi/string/{00020329-0000-0000-C000-000000000046}/".

Can anyone confirm problems with this option?
Is there a solution for this? Turning the option off works as a workaround.

Thanks in advance!


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