Standard cost Estimate not picking material price from PO

Hi friends,

After June standard costing for May closing, 2 materials were updated with PO prices, and some did not.

In the same PO, the other materials are picking the PO price.

I have this peculiar issue.

This happened only for one Month - June, 2010. From July 2010 it has picked the PO price.

Kindly suggest the steps to be verified in different angle for this reason and problem.

Thanks & regards

srinivas panchakarla