Issue with Outlook custom properties in shared calendar appointments

Question

I am using VBA to add an appointment to a shared calendar that includes a custom property, here's an example of the code:

Dim objOutlook As Object
Dim objNamespace As Object
Dim objCalendar As Object
Dim objAppointment As Object
Dim vPropPath  As String

Set objOutlook = GetOutlookApp()
Set objNamespace = objOutlook.GetNamespace("MAPI")
Set objCalendar = GetOutlookCalendar()

Set objAppointment = objCalendar.items.Add(1)

objAppointment.Subject = vTitle
objAppointment.Body = vBody

vPropPath = "http://schemas.microsoft.com/mapi/id/{00020329-0000-0000-C000-000000000046}/7771001F"
objAppointment.PropertyAccessor.SetProperty vPropPath, "1"

objAppointment.Save
objAppointment.Close 0 

Set objAppointment = Nothing
Set objCalendar = Nothing
Set objNamespace = Nothing
Set objOutlook = Nothing

When I check the custom property of the created appointment, it is present initially. However, after Outlook syncs with the Exchange server or when the appointment is edited, the custom property is removed. Thanks in advance.