Reservation

Hi,

I'm traying to use reservation but the first issue regarding them was the inventory.

I created a Sales Order no. 5000 with qty 6, my inventory in item ledger entry was 5 and I had a purchase order with qty 2. I reserved 5 qty form item ledger entry and 1 qty from purchase order.

I created oneother Sales Order no. 5001 with qty 3.  I do not reserved any thing. I posted  the SO 5001 before SO no. 5000.

System do not prevent me to post. 

So I'm not clear which is the meaning of nav reservation? Because i reserved the inventory on SO no. 5000