TAX code and Tax rate overwritten in SAP PO

Hi All,

Scenario is

1. Condtion type are as below in PO

1. pbxx

2. zco

3. ZNAV--Condition records are maintained and set tax code  'VA' and 19% on sum of pbxx and zco

3. mwvs--In pricing set up is no manual setting and tax rate and code should be taken from condition record

Now we create po using BAPI..and tax code is 'V0' is passed to bapi and expecting tax rate should come from FTXP.

i opened PO and observed that  tax code V0 has come under invoice tab.but tax code and  rate  to MWVS taking from ZNAV cond type ( tax code 'VA' and  rate19%).

i wan for condition type MWVS , tax code should be VO and  tax rate 10% kept for MWVS in FTXP .

Why SAP system considering condition record instead tax code passed to BAPI.

Regards

Ramakrishnaiah Y