MRP available Qty and reservation not working

Question

Hi PP gurus
lets say I have material A that use component B in qty 1 to be manufactured, the problem is the following
1) If I have 3 orders for Material A with dates say
01-Mar-2011 Order 1
15-Mar-2011 Order 2
28-Mar-2011 Order 3
And I have in available stock only 1 piece of material B I can therefore only release order 1, If I try to release order 2 then I get an error because the material is not available (this is what I want and is working well)
The problem comes when I go and change the date of order 2 to 15-Feb-2011 (to any previous date from order 1)now I'm able to release, and same happens if I change the date of order 3 to 10-Feb-2011 then I can release order 3 too and this is not correct, I need to release orders only If I have the components available and no hard reservations for it.
Note: when I'm able to release also if I check the material availability it says all materials in order XXX are available
Note2: I have setting for only releasing if no missing components
Please advise what settings are missing to achieve this
Regards

Answer 1

A few pointers which should help correct the situation:
First reset all commitments done to the 3 SFO's. If its a test system, then do a re-read of master data if no postings are done, so you can revert back to your initial status.
Now run Av. check for all three orders in COMAC. Depending on the settings done in OPJJ for the checking rule, system will do the commitments. Once the commitments are done, check in the 3 orders, whether the committed qty field is populated. If you're only considering stock in the checking rule, then system would commit to the first order.
Now change date of the 2nd or 3rd order to an earlier date. Now if you run an av. check within that specific order, system will show it as shortage (provided you do not make any changes to checking rule in between).
But if you re-run Av. check in COMAC with reset commitments flagged, then system will reset previous commitments n commit to the rescheduled order.
In your check rule, ensure that you're considering reservations in inward/outward mvts. & also see if any supply elements such as PO, PR etc is considered. If they are considered, then it might well be that system is committing all 3 orders as there are some supply elements.
If the above still does not resolve the issue, then upload screenshots of MD04, MMBE, CO03 (component view), OPJJ to a portal n paste link here.