diff --git a/tiramisu/setting.py b/tiramisu/setting.py
index 5951c73..4112419 100644
--- a/tiramisu/setting.py
+++ b/tiramisu/setting.py
@@ -124,7 +124,7 @@ class OptionBag:
                  'config_bag',
                  'ori_option',  # original option (for example useful for symlinkoption)
                  'properties',  # properties of current option
-                 'apply_requires',
+                 'apply_requires',  # apply requires or not for this option
                  'fromconsistency'  # history for consistency
                  )
 
@@ -147,7 +147,8 @@ class OptionBag:
     def __getattr__(self, key):
         if key == 'properties':
             settings = self.config_bag.context.cfgimpl_get_settings()
-            self.properties = settings.getproperties(self, apply_requires=self.apply_requires)
+            self.properties = settings.getproperties(self,
+                                                     apply_requires=self.apply_requires)
             return self.properties
         elif key == 'ori_option':
             return self.option
@@ -189,6 +190,11 @@ class ConfigBag:
     def set_permissive(self):
         self.properties = frozenset(self.properties | {'permissive'})
 
+    def __delattr__(self, key):
+        if key == 'properties':
+            return
+        raise KeyError('unknown key {} for ConfigBag'.format(key))
+
     def copy(self):
         kwargs = {}
         for key in self.__slots__:
@@ -689,6 +695,16 @@ class Settings(object):
 
     #____________________________________________________________
     # validate properties
+    def calc_raises_properties(self,
+                               option_properties,
+                               config_properties,
+                               config_permissives):
+        properties = option_properties & config_properties - {'frozen', 'mandatory', 'empty'}
+        # remove global permissive properties
+        if properties and ('permissive' in config_properties):
+            properties -= config_permissives
+        # at this point an option should not remain in properties
+        return properties
 
     def validate_properties(self,
                             option_bag):
@@ -702,14 +718,9 @@ class Settings(object):
         config_bag = option_bag.config_bag
         if not config_bag.properties:
             return
-        # calc properties
-        properties = option_bag.properties & config_bag.properties - {'frozen', 'mandatory', 'empty'}
-
-        # remove permissive properties
-        if properties and ('permissive' in config_bag.properties):
-            # remove global permissive if need
-            properties -= config_bag.permissives
-        # at this point an option should not remain in properties
+        properties = self.calc_raises_properties(option_bag.properties,
+                                                 option_bag.config_bag.properties,
+                                                 option_bag.config_bag.permissives)
         if properties != frozenset():
             raise PropertiesOptionError(option_bag,
                                         properties,