Item Sequence in Bill of material issue in Oracle EBS.

Hello Team,

we have Bill of material ABC where we have component lets say 1234 added manually and having Item Sequence = 10

further we have created ECO though interface process which contains same BOM item ABC and having different child component with add action. when ECO got created it has added an Items 789, 901, 121, 234 with Item seq value as 9, 10, 11, 12 under bom ABC.

which in result we now have manually created item 1234 with Item seq - 10

and item 901 created through ECO having same item Seq 10.

why system allowed to have same Item seq for different items under same bill.

can't we have the Unique Item seq number with the single BOM item.?