Calendar requests sent to resource mailbox have no content

I have been trying to work out why calendar invitations sent to room mailboxes have the content stripped out.  I now understand that this is applied to all resource mailboxes by default.  I have changed this by using the Set-CalendarProcessing cmdlet to change the value of the DeleteComments parameter:

Set-CalendarProcessing -Identity "BoardRoom" -DeleteComments $false

Now the calendar entries in the room mailbox contain the content.