Average Cost not correct in sales by item report: Analyse Sales [Item]

We have 2 item codes that are not showing correctly in my sales reports in regards to Avg Cost.

1 Item: Average Cost over 2 historical PO's is $3.67.  The average cost show in MYOB under Item List, and is averaged out over 2 PO's.  Analyse Sales (Item) report shows $5.04.

2nd Item: Some stock recieved free of charge replacment (4800 recieved in at $0 and 3200 units recieved in at $4.74.)  So average cost should show as $1.22 (and shows in the item detail) but its showing as $5.60 in Analyse Sales report.