diff --git a/test/test_config.py b/test/test_config.py
index df3b84d..b50b7d0 100644
--- a/test/test_config.py
+++ b/test/test_config.py
@@ -187,3 +187,15 @@ def test_has_value():
     assert not g5 in config.cfgimpl_get_values()
     config.od.g5 = 'yes'
     assert g5 in config.cfgimpl_get_values()
+
+
+def test_values_not_setitem():
+    g1 = IntOption('g1', '', 1)
+    g2 = StrOption('g2', '', 'héhé')
+    g3 = UnicodeOption('g3', '', u'héhé')
+    g4 = BoolOption('g4', '', True)
+    g5 = StrOption('g5', '')
+    d1 = OptionDescription('od', '', [g1, g2, g3, g4, g5])
+    root = OptionDescription('root', '', [d1])
+    config = Config(root)
+    raises(ValueError, "config.cfgimpl_get_values()[g1] = 2")
diff --git a/test/test_option_consistency.py b/test/test_option_consistency.py
index 72aeadb..8dde2a8 100644
--- a/test/test_option_consistency.py
+++ b/test/test_option_consistency.py
@@ -133,6 +133,7 @@ def test_consistency_ip_netmask_multi_master():
     c.b = ['255.255.255.255']
     c.b = ['255.255.255.0']
     raises(ValueError, "c.a = ['192.168.1.0']")
+    c.a = ['192.168.1.2', '192.168.1.3']
 
 
 def test_consistency_network_netmask_multi_master():
diff --git a/test/test_option_owner.py b/test/test_option_owner.py
index dbefd07..eb3790a 100644
--- a/test/test_option_owner.py
+++ b/test/test_option_owner.py
@@ -5,6 +5,7 @@ from tiramisu.setting import owners
 from tiramisu.config import Config
 from tiramisu.option import ChoiceOption, BoolOption, IntOption, FloatOption, \
     StrOption, OptionDescription
+from tiramisu.error import ConfigError
 
 
 def make_description():
@@ -70,3 +71,18 @@ def test_setowner_without_valid_owner():
     assert cfg.dummy is False
     assert cfg.getowner(gcdummy) == 'default'
     raises(TypeError, "cfg.cfgimpl_get_settings().setowner('gen_config')")
+
+
+def test_setowner_for_value():
+    gcdummy = BoolOption('dummy', 'dummy', default=False)
+    descr = OptionDescription('tiramisu', '', [gcdummy])
+    cfg = Config(descr)
+    assert cfg.dummy is False
+    assert cfg.getowner(gcdummy) == 'default'
+    owners.add_owner("new")
+    raises(ConfigError, "cfg.cfgimpl_get_values().setowner(gcdummy, owners.new)")
+    cfg.dummy = False
+    assert cfg.getowner(gcdummy) == owners.user
+    cfg.cfgimpl_get_values().setowner(gcdummy, owners.new)
+    assert cfg.getowner(gcdummy) == owners.new
+    raises(TypeError, "cfg.cfgimpl_get_values().setowner(gcdummy, 'new')")
diff --git a/test/test_parsing_group.py b/test/test_parsing_group.py
index 5f4985c..7b9dffe 100644
--- a/test/test_parsing_group.py
+++ b/test/test_parsing_group.py
@@ -180,6 +180,9 @@ def test_values_with_master_and_slaves():
     assert cfg.ip_admin_eth0.netmask_admin_eth0 == [None]
     assert cfg.getowner(ip_admin_eth0) == owner
     assert cfg.getowner(netmask_admin_eth0) == owners.default
+    cfg.ip_admin_eth0.ip_admin_eth0 = ["192.168.230.145", "192.168.230.147"]
+    raises(SlaveError, 'cfg.ip_admin_eth0.netmask_admin_eth0.append(None)')
+    raises(SlaveError, 'cfg.ip_admin_eth0.netmask_admin_eth0.pop(0)')
 
 
 def test_reset_values_with_master_and_slaves():
@@ -395,3 +398,12 @@ def test_multi_extend_master():
     cfg.read_write()
     raises(SlaveError, "cfg.ip_admin_eth0.ip_admin_eth0.extend(['ok'])")
     raises(SlaveError, "cfg.ip_admin_eth0.netmask_admin_eth0.extend(['ok'])")
+
+
+def test_multi_non_valid_value():
+    ip_admin_eth0 = StrOption('ip_admin_eth0', "ip réseau autorisé", multi=True)
+    maconfig = OptionDescription('toto', '', [ip_admin_eth0])
+    cfg = Config(maconfig)
+    cfg.read_write()
+    cfg.ip_admin_eth0 = ['a']
+    raises(ValueError, 'cfg.ip_admin_eth0[0] = 1')
diff --git a/tiramisu/setting.py b/tiramisu/setting.py
index 25e9485..3c649fe 100644
--- a/tiramisu/setting.py
+++ b/tiramisu/setting.py
@@ -223,7 +223,7 @@ class Settings(object):
         return Property(self, self._getproperties(opt, path), opt, path)
 
     def __setitem__(self, opt, value):
-        raise ValueError('you must only append/remove properties')
+        raise ValueError('you should only append/remove properties')
 
     def reset(self, opt=None, _path=None, all_properties=False):
         if all_properties and (_path or opt):
diff --git a/tiramisu/value.py b/tiramisu/value.py
index 9535869..fb62698 100644
--- a/tiramisu/value.py
+++ b/tiramisu/value.py
@@ -218,8 +218,7 @@ class Values(object):
         return value
 
     def __setitem__(self, opt, value):
-        path = self._get_opt_path(opt)
-        self.setitem(opt, value, path)
+        raise ValueError('you should only set value with config')
 
     def setitem(self, opt, value, path, force_permissive=False,
                 is_write=True):
@@ -409,16 +408,9 @@ class Multi(list):
                         dvalue = values._getcallback_value(slave, index=index)
                     else:
                         dvalue = slave.impl_getdefault_multi()
-                    old_value = values.getitem(slave, path,
-                                               validate_properties=False)
-                    if len(old_value) < self.__len__():
-                        values.getitem(slave, path,
-                                       validate_properties=False).append(
-                                           dvalue, force=True)
-                    else:
-                        values.getitem(slave, path,
-                                       validate_properties=False)[
-                                           index] = dvalue
+                    values.getitem(slave, path,
+                                   validate_properties=False).append(
+                                       dvalue, force=True)
 
     def sort(self, cmp=None, key=None, reverse=False):
         if self.opt.impl_get_multitype() in [multitypes.slave,