Bapi_acc_document_post with VST tax

Question

I've been using this bapi for some time with US tax codes and now need to make it work with Canadian codes.
The Canadian tax codes in our system are set as 'Deductible' (T007B-STAZF 'tax not deductible' is left blank).
I am passing tax information in AccountTax to the bapi and the same line is also in CurrencyAmount.
There is a place in the code where the tax line is not eliminated from table it_acccr because it is not considered NAV or NVV (stazf is not eq to 'X'). 
This causes the bapi to think the document is out of balance by the amount of the tax.
Example:
AccountGL 
10   154000 (for the tax)
20   476000 (for the expense)
30   113100 (for the offset)
AccountTax
10000000  154000  MWVS    VST   V1
CurrencyAmount
10       14.89  (the tax)
20       85.11  (the expense)
30     -100.00 (the offset)
10000000 14.89 (for the tax entry)
If the tax is NAV or NVV the forth line is deleted and 10 - 30 are used to determine balance - no problem. When VST all four lines are used to determine balance and balance is then not zero.
If feel that I must not understand VST taxes and am doing something wrong in setting up the tables to send to the BAPI.  Can any one shed light?
I have searched and searched OSS and have not seen anything addressing this.

Answer 1

There is an entry in AccountTax table
Itemno_acc  0010000000
GL_account  0000154000
Cond_Key    MWVS
Acct_Key    VST
Tax_code    V1
Tax_Rate    175.000
There is a corresponding entry in CurrencyAmount
Itemno_acc   0010000000
Currency     GBP
Amt_Doccur   14.89
Amt_base     85.11
I'm following the exact same format as when the tax acct key is NVV.