Create Consumption Advice ，How to calculate the result

I have two materials，The same settings ，I do the following：

item1 Quantity price item2 Quantity price

A 10 1 B 10 1

20 2 20 2

30 3 30 3

Create a purchase order ，The same quantity in storage

the number of sub inventory transfers is as follows

item1 Quantity item2 Quantity

A 20 B 19

B 1

run the Create Consumption Advice

when I found

item1 Issued quantity pice item2 Issued quantity pice

A 20 40 B 19 19

any other know ,the Create Consumption Advice how to word ,why item2 One quantity is missing，