validators.diff

diff --git i/modules/market/mk_forms.py w/modules/market/mk_forms.py
index dd3646a..e78a8d8 100644
--- i/modules/market/mk_forms.py
+++ w/modules/market/mk_forms.py
@@ -6,6 +6,8 @@ modules/market/mk_forms.py
 Created by Christian Klein on 2015-12-01.
 Copyright (c) 2015 HUDORA GmbH. All rights reserved.
 """
+import logging
+
 import huTools.checksumming
 import wtforms
 
@@ -28,6 +30,10 @@ class UniqueMPN(object):
             mk_Product.mpn == field.data)
         product = query.get()
         if product and product != self.product:
+            logging.debug("product: %r", product )
+            logging.debug("self.product: %r", self.product)
+            logging.debug("self.source.source_id:%r", self.source.source_id,)
+            logging.debug("field.data:%r", field.data)
             raise wtforms.validators.ValidationError(u'MPN muss eindeutig sein')
 
 
@@ -47,6 +53,7 @@ class BrandValidator(object):
     def __call__(self, form, field):
         """Überprüfe, ob der Lieferant die angegebene Marke vertreiben darf."""
         if field.data not in self.source.brands:
+            logging.debug("%r %r %r", self.source.source_id, self.source.brands, field.data)
             raise wtforms.validators.ValidationError(
                 u'Sie haben keine Berechtigung für die Marke {}'.format(field.data))
 
@@ -57,7 +64,7 @@ ProductForm = model_form(
     mk_Product,
     only=['name', 'brand', 'description', 'gtin13', 'preis', 'menge_verfuegbar', 'liefertage', 'sperrgut'],
     field_args=dict(
-        gtin13=dict(label=u'GTIN-13', validators=[ean_validator, wtforms.validators.Optional()]),
+        gtin13=dict(label=u'EAN', validators=[ean_validator, wtforms.validators.Optional()]),
     )
 )
 
@@ -85,6 +92,7 @@ def get_form(source, product=None, *args, **kwargs):
     Fügt dynamisch erzeugten Validator für MPN ein.
     """
     form = ProductCreateForm(*args, **kwargs)
+    logging.debug("get_form: %r", source.source_id)
     form.mpn.validators.append(UniqueMPN(source, product=product))
     form.brand.choices = [(brand, brand) for brand in source.brands]
     form.brand.validators.insert(0, BrandValidator(source))
diff --git i/modules/market/mkb_views.py w/modules/market/mkb_views.py
index ff0aa39..070c35f 100644
--- i/modules/market/mkb_views.py
+++ w/modules/market/mkb_views.py
@@ -113,18 +113,21 @@ class ListProducts(AuthenticatedHandler):
 class ShowProduct(AuthenticatedHandler):
     """Produkt Administrationanzeigen"""
 
-    def get(self, source_id, sku, fmt='html'):
-        """Template anzeigen"""
-        source = mk_models.get_source(source_id)
-
+    def get_product(self, source_id, sku):
+        assert self.source.source_id == source_id
         product = mk_models.mk_Product.get_by_id(sku)
         if not product:
             raise gaetk.handler.HTTP404_NotFound
         elif product.source != source_id:
             raise gaetk.handler.HTTP403_Forbidden
+        return product
+
+    def get(self, source_id, sku, fmt='html'):
+        """Template anzeigen"""
+        product = self.get_product(source_id, sku)
 
         if not product.liefertage:
-            product.liefertage = source.liefertage_default
+            product.liefertage = self.source.liefertage_default
 
         self.multirender(
             fmt, dict(product=product),
@@ -137,15 +140,7 @@ class ShowProduct(AuthenticatedHandler):
 
     def post(self, source_id, sku, fmt='html'):
         """Formular validieren"""
-        source = mk_models.get_source(source_id)
-        if source.key != self.credential.source:
-            raise gaetk.handler.HTTP403_Forbidden
-
-        product = mk_models.mk_Product.get_by_id(sku)
-        if not product:
-            raise gaetk.handler.HTTP404_NotFound
-        elif product.source != source_id:
-            raise gaetk.handler.HTTP403_Forbidden
+        product = self.get_product(source_id, sku)
 
         # TODO: Das ist noch ein bisschen hacky:
         self.request.POST.add('mpn', product.mpn)
@@ -153,6 +148,8 @@ class ShowProduct(AuthenticatedHandler):
         form = mk_forms.get_form(self.source, product=product, formdata=self.request.POST, mpn=product.mpn)
         if form.validate():
             form.populate_obj(product)
+            if product.liefertage == self.source.liefertage_default:
+                product.liefertage = None
             product.put()
             raise gaetk.handler.HTTP302_Found(location='/mkb/{}/p/{}.{}'.format(source_id, sku, fmt))