Hi! That’s weird. I have a tried both a fresh install and on a live project and I get the same result on both of them.
Have you really tried to mark the order in WooCommerce as Complete efter you moved the ticket?
If I move a ticket to a new event and then mark the order in WooCommerce as Complete I still get an attendee count on the old event.
But I will run the test for conflicts and send the results to you.
Thanks