=== modified file 'account/invoice.py'
--- account/invoice.py	2010-11-04 18:33:33 +0000
+++ account/invoice.py	2010-11-23 11:44:27 +0000
@@ -1214,24 +1214,43 @@
         'tax_amount': fields.float('Tax Code Amount', digits=(16,int(config['price_accuracy']))),
     }
     
+    def _calculate_factor(self, cr, uid, ids, factor_name):
+        factor = 1
+        invoice_tax_obj = self.browse(cr, uid, ids[0])
+        if factor_name == 'factor_base':
+            if invoice_tax_obj.base <> 0.0:
+                factor = invoice_tax_obj.base_amount / invoice_tax_obj.base
+        
+        elif factor_name == 'factor_amount':
+            if invoice_tax_obj.amount <> 0.0:
+                factor = invoice_tax_obj.tax_amount / invoice_tax_obj.amount
+
+        return factor
+    
     def base_change(self, cr, uid, ids, base,currency_id=False,company_id=False,date_invoice=False):
         cur_obj = self.pool.get('res.currency')
         company_obj = self.pool.get('res.company')
-        company_currency=False
+        company_currency = False
+        factor = 1
+        if ids:
+            factor = self._calculate_factor(cr, uid, ids, 'factor_base')
         if company_id:            
             company_currency = company_obj.read(cr,uid,[company_id],['currency_id'])[0]['currency_id'][0]
         if currency_id and company_currency:
-            base = cur_obj.compute(cr, uid, currency_id, company_currency, base, context={'date': date_invoice or time.strftime('%Y-%m-%d')}, round=False)
+            base = cur_obj.compute(cr, uid, currency_id, company_currency, base*factor, context={'date': date_invoice or time.strftime('%Y-%m-%d')}, round=False)
         return {'value': {'base_amount':base}}
 
     def amount_change(self, cr, uid, ids, amount,currency_id=False,company_id=False,date_invoice=False):
         cur_obj = self.pool.get('res.currency')
         company_obj = self.pool.get('res.company')
-        company_currency=False
+        company_currency = False
+        factor = 1
+        if ids:
+            factor = self._calculate_factor(cr, uid, ids, 'factor_amount')
         if company_id:
             company_currency = company_obj.read(cr,uid,[company_id],['currency_id'])[0]['currency_id'][0]
         if currency_id and company_currency:
-            amount = cur_obj.compute(cr, uid, currency_id, company_currency, amount, context={'date': date_invoice or time.strftime('%Y-%m-%d')}, round=False)
+            amount = cur_obj.compute(cr, uid, currency_id, company_currency, amount*factor, context={'date': date_invoice or time.strftime('%Y-%m-%d')}, round=False)
         return {'value': {'tax_amount':amount}}
     
     _order = 'sequence'