Item valuation being updated to a wrong value

[Mg1988]

hi i have made 4 transaction, in erpnext,

purchase being receive for the first 3 item have no problem,

but on the 4th purchase receipt, the valuation goes up,

but nothing is change,

item price bought is the same.

causing problems in the cost of goods sold when item being delivered .

[Mg1988]

here is the stock ledger after i made the delivery,