Product stock completely wrong after splitting orders

I was testing whether stock mutations are as expected when splitting orders with this plugin. I was shocked to find out that the stock gets completely messed up from the split order option.

I have product X, 8 on stock. If I have an order with Product X, quantity 10x, the normal response is to decrease stock with 10, so stock becomes -2. The order is “in procesing”.

I can only deliver 8 out of 10. So I split the order, the new order gets Product X, quantity 2x. I delivered the first 8, so the original order I move the status to “Completed”.

Now suddenly the stock increased by 2 and becomes 0, while it’s supposed to stay the same! I think it increases it because it somehow detects that 2 products are not in the order anymore? Anyway, the new, splitted order, I would put “On hold” until I can deliver them. Then, when I can deliver the rest of the product (2x), I would move the status of the new order to “Completed”. Now the stock INCREASES again, this time with +8, and even though I have delivered 10 items, my stock is now exactly the same as it was before the order ever got placed.

Needless to say, I am not going to be using this plugin anymore.

WP 6.9.4.
WooCommerce 10.9.4.
Order Splitter version: free 1.4.11