diff --git a/tiramisu/config.py b/tiramisu/config.py
index 3f725c9..84f1cc4 100644
--- a/tiramisu/config.py
+++ b/tiramisu/config.py
@@ -161,13 +161,13 @@ class Config(object):
 
     def _get_master_len(self, slave_name):
         try:
-            parent_cfg = self._cfgimpl_parent
+            parent_cfg = self
             if parent_cfg is None:
                 return None
             master_name = parent_cfg._cfgimpl_descr.get_master_name()
-            master_value = getattr(parent_cfg, master_name)
+            master_value = parent_cfg._cfgimpl_values[master_name]
             return len(master_value)
-        except TypeError:
+        except TypeError, err:
             # in this case we just don't care about the len
             return None
 
@@ -176,8 +176,8 @@ class Config(object):
         if master_len == None:
             return True
         if master_len != len(slave_value):
-            raise ValueError("invalid len for the group {0}"
-                    "in the option {1} ".format(master_name, slave_name))
+            raise ValueError("invalid len for the group of"
+                    " the option {0}".format(slave_name))
 
     def fill_multi(self, name, result, default_multi=None):
         """fills a multi option with default and calculated values
diff --git a/tiramisu/option.py b/tiramisu/option.py
index 96625b9..d49013d 100644
--- a/tiramisu/option.py
+++ b/tiramisu/option.py
@@ -63,14 +63,18 @@ class Multi(list):
             if master != self.opt._name:
                 raise IndexError("in a group with a master, you mustn't add "
                         "a value in a slave's Multi value")
-            for name, multi in self.config:
-                if master == multi.opt._name:
-                    multi._setvalue(value, who=settings.owner)
-                else:
-                    default_value = multi.opt.getdefault_multi()
-                    multi._setvalue(default_value)
         except TypeError:
-            self._setvalue(value, who=settings.owner)
+            return self._setvalue(value, who=settings.owner)
+        multis = []
+        for name, multi in self.config:
+            multis.append(multi)
+        for multi in multis:
+            if master == multi.opt._name:
+                ret = multi._setvalue(value, who=settings.owner)
+            else:
+                default_value = multi.opt.getdefault_multi()
+                multi._setvalue(default_value)
+        return ret
 
     def _setvalue(self, value, key=None, who=None):
         if value != None:
@@ -96,19 +100,24 @@ class Multi(list):
             if master != self.opt._name:
                 raise IndexError("in a group with a master, you mustn't remove "
                         "a value in a slave's Multi value")
-            for name, multi in self.config:
-                if master == multi.opt._name:
-                    multi._pop(key)
-                else:
-                    change_who = False
-                    # the value owner has to be updated because
-                    # the default value doesn't have the same length
-                    # of the new value
-                    if len(multi.opt.getdefault()) >= len(multi):
-                        change_who = True
-                    multi._pop(key, change_who=change_who)
         except TypeError:
-            self._pop(key)
+            return self._pop(key)
+
+        multis = []
+        for name, multi in self.config:
+            multis.append(multi)
+        for multi in multis:
+            if master == multi.opt._name:
+                ret = multi._pop(key)
+            else:
+                change_who = False
+                # the value owner has to be updated because
+                # the default value doesn't have the same length
+                # of the new value
+                if len(multi.opt.getdefault()) >= len(multi):
+                    change_who = True
+                multi._pop(key, change_who=change_who)
+        return ret
 
     def _pop(self, key, change_who=True):
         oldvalue = list(self)
@@ -527,7 +536,7 @@ class OptionDescription(HiddenBaseType, DisabledBaseType):
 
     def get_master_name(self):
         if self.master is None:
-            raise TypeError('get_master_name() shall not be called in case of'
+            raise TypeError('get_master_name() shall not be called in case of '
                 'non-master OptionDescription')
         return self.master
     # ____________________________________________________________