Material Determination Issue while posting billing document.

I am taking about the standard process of SAP.
Just try entry with Outcome as A while defining substitute
reason and then process the order.
It will show both the old and new material with item
category as TAX and TAPS respectively.
TAX for non- stock item- means as of now the material is not
available.
TAPS- the new material which has replaced the old material.


Now, if you will see the configuration of item category TAX
and TAPS in IDES, it would be more clearer as I mentioned in
the first update.


The only issue is - I am facing a problem in billing.




Now if you re-consider my post, I guess it would be more
clearer.




However, the issue is that in billing its not showing the
right price.
Please suggest.

Configuration -
Item category- TAX- Old material.
Billing relevance- A
Stats- X
Pricing- NO

Item Category- TAPS- New materail
Billing Relevance- A
Stats- NO
Pricing- Yes

Because I want both the material in billing, so billing
relevance is A.
And I want the price of new material so for TAPS pricing -
Yes.

But every time I am trying system is taking the price of
TAX. Not sure why?

If I make it as vice- verse, thinking lets take the price of
new material, now the system is taking the price of old .