Excise Base value calculated wrongly in GR

Dear experts,

When preparing Bought out goods receipt in migo,excise base value is coming wrongly(not as per PO) in sometimes.

If we come back from the screen without saving & then try again. That time the base value is calculating correctly.

This kind of situation is arising inconsistantly. Not regularly.

Please suggest to overcome this issue.

Regards

M.Sarathi