Hi,
Just cross check following to get clear about concept which cause your concern
You created new material with price control V and the price 10 $ and receipt 10 Pieces of material with 501 movement type (goods receipt)
Cross check accounting document with stock of material with material value
You changed the price of material with new price is 15 $ in t.code:MR21 .
Just check accounting document for material with t.code: MR51 and find stock of material with material value
Again you have taken 10 Pieces of material with 501 movement type to the same storage (goods receipt).
Now Cross check accounting document with stock of material with material value.
You send one Piece of material with 201 movement type (goods issue) and now Cross check accounting document with stock of material with value where system calculating perfectly with average material price is 15 $ @ t.code:MM03
NOTE:
When you change material price in t.code:MR21, the accounting triggers with G/L account of Gain/loss from revaluation (with UMB key) against your Inventory account
Regards,
Biju K