Wrong commitment item while posting GR

Dear all,

We have created a PO with account assignment category-K and assigned a expenses G/L to it.While doing GRN entry the system is posting the document with the commitment item of the expenses G/L in the GR/IR clearing G/L.

for example

in the expenses G/L commitment item is 9000-30/3

In the GR/IR G/L commitment item is 4000 - 40/3

In both the cases commitment item is derived from the G/L master.

The document is posted as

Expenses G/L Dr. with commitment item-9000

GR/IR Cr. with commitment item - 9000 also.

we are not able to identify why system is behaving like this.

Regards,

Shivaji