We are able to take an MO from Complete status to released status by doing one of the following.
1. Changing the status using the drop-down in the MO entry window.
2. Reversion the MO receipt using the Manufacturing Order Receipt Entry window.
If the second method is used I don't run into any trouble getting the MO back to Complete. But, if the first option is used I can't complete the MO unless I increase the quantity on the MO by 1, do a MO receipt entry, then adjust the inventory this creates back out of inventory.