Hi Dan!
Thanks for reaching out to us! 🙂
I don’t think you are doing anything wrong here. That is a default behaviour from WooCommerce and Event tickets pulls that information from there.
It may not make much sense not increasing the stock when an order has been cancelled when selling tickets. But if you are selling products that you ship to customers, the reason to cancel an order could be it never arrived or it was broken, so that would diminish the stock.
Does it make sense to you know? Let me know if you have any other questions.
Best!
Victor