TAX CODE COMBINATION Problem in PO

Dear Gurus

I have maintained conditions for tax in FV11 for tax code (Material,(A) Plant(B) and tax code(T1) combination)T1-JMOP-16%,JSEP-1% and JEC1-2%,JVRD-4%

I have created second tax code T2 and maintained conditons in FV11 with plant(B) and tax code(T2) combination and maintained JVRD -4%

when i am making PO and selecting tax code T1 system is calculating Tax with Tax code T1

But when i am selecting tax code T2 in PO system is still calculating tax with the tax conditions maintained in FV11 for T1 but not for T2

Can u plz tell me how to resolve this problem

Regds

shail