Backward Item card make same 2 lines item ledger entry.

Hi Nav Expert.

I  always found that the backward item always make 2 lines for same code in item ledger entry. I set the A Item as Backward.  A is one of  Production Bom Line  qty 4.  but when we post the output journal , the actual consumption calculated qty 8. it cause from the item ledger entry make it 2  lines  .

2184   R00ZA    01/18/13 Consumption 20313  E2130071   E2   -4 0    -4 0 No   No Item No     01/18/13    ........   

2185   R00ZA    01/18/13 Consumption 20313   E2130071   E2   -4 0   - 4 0 No   No Item No     01/18/13   .........  

pls help me for this solution .

thks

Alfian 98