K item cat. in BOM and get duplicated in sales order

Hi,

I create a configurable material and use class as its BOM..While configuring this material,K class is duplicated in CU50 or VA01..but it's good in the planned order after running MRP...

What's the probable reason for it?thanks..

Look,0040 is duplicated and i should only see one of them.

After MRP,the planned order is fine..only one item is chosen...

Class: