4.07.6 WO does not do costing properly

[ronwong]

Used to work a few versions ago.

Product A Product B Ttl
unit cost before 2.05 1.48 606.04
Units before 196 138
unit cost after 2.05 1.507517241 606.04
Units After 189 145
Wrong cost after 2.05 2.05

The above summarize what I tried to do.
Product B is manufactured
1 product A makes 1 product B.
I manufacture 7 units of A to B. After manufacture, 7 units of A should move over with unit cost 2.05 thus bring up the average cost of B from 1.48 to 1.507 so that total A and B total cost remains at 606.04.
But it took over the Product A cost of 2.05.

Did I do something wrong?
set product B as manufactured.
set up BOM.
Open WO, receive items, update costing, close WO.