Account Distribution is not correctly executed on the AP invoice

Hi All,
I have created AP invoice with two lines and one tax line of 30
1) First line with an amount of 70
2) Second Line with an amount of 30.
3) Third Line as Tax for an amount of 30

When i view the allocation , I got the allocated amount as 21 and 9 for both the lines which is correct but when i view the distributions , I see that the distribution for line with an amount of $21 and $9 is referring to the account on the first Item Line.
Which is not the expected behavior.
Expected behaviour:
For line item 1 , what ever is the distribution account that should be shown for the $21 line and whatever is the line item 2 distribution,  that should be shown for $9 line.