Cost changed when PO return

Business Central/NAV User Forum
1

Hi guys,

I’m a newbie in Navision 2009 - and need advice for this situation :

My item No is R100. In prior inventory period unit cost of this item is 8.00

In the next inventory period I do a Purchase Return order to return a PO which is inputed in prior inventory period
I use function get posted document lines to reverse.Next I run ACIE. Now I see unit cost of this item changed from 8.00 to 8.20 in prior inventory period

I use average costing method.

I don’t know why and how unit cost of a item can not change in prior inventory when I do PO return in next inventory period?

Thanks in advance.