Hi, I´m using Odoo Saas

I have just switched to 2-step delivery process. 

I am founding an odd behaviour as follows:

1. I sell 10 units

2. I manufacture 10 units

3. I store 10 units after production

4. Picking for delivery shows 10 units in demand but 9 in quantity, and product shows as "not available". When I go to the availability report, it shows 9 units are reserved, and 1 unit is "in transit". So I have to manually change to 10 units in the quantity column, then product shows as "available" and I am able to proceed with a Delivery order of 10 units.

I don´t understand why 1 unit is being left behind / stuck "in transit".