Order Status Change Increasing Product Quantity

Here is my headache. Took me a while to debug it to here, but now I am stumped. Person places an order for an item we manufacturer. Order status changes to PAID and the inventory is decreased. Great, working as planned. Now if we have it in stock packaged, we change to preparing for shipment and shipped, quantity stays reduced. Working as planned. My problem is we created an additional status called PARTS, which is for items that are conceptually on backorder or at least not packaged. When we change the status from PAID to PARTS, it increases the quantity of the product in the system. The order status identified for PARTS status is T in case it ends up being relevant. Now I know in order status, there is an option to increase or decrease inventory. I checked and it was indeed set to decrease. I changed it to increase, saved then back to decreased and saved just to make sure. No effect. Verified in the database is it stored as 'D' for decrease. Still not working. It always increases the product quantity and then decreases is when I change back to paid. Any idea if there is code somewhere else in here, maybe that relates to the 'T' status as something else that would normally increase it? Thanks for any help or ideas.

Try to change it directly in database to 'I'

Try to change it directly in database to 'I'

Only other available letter is 'N' which I know is hardcoded for incomplete. All of the other A-Z are taken.

I do not mean the order status letter, but value of the "inventory" column

I do not mean the order status letter, but value of the "inventory" column

No change regardless of whether that value is D or I, inventory increases with both on a status change.

It is strange. Did you clear cache after direct changes in the database?