diff --git a/mushroom_rl/core/extra_info.py b/mushroom_rl/core/extra_info.py
index bcfcea4a..1b1faf75 100644
--- a/mushroom_rl/core/extra_info.py
+++ b/mushroom_rl/core/extra_info.py
@@ -113,10 +113,16 @@ def flatten(self, mask=None):
         info._structured_storage = {}
 
         for key in self.data:
-            info.data[key] = info._array_backend.pack_padded_sequence(self.data[key], mask)
+            if mask is None:
+                info.data[key] = info._array_backend.flatten(self.data[key])
+            else:
+                info.data[key] = info._array_backend.pack_padded_sequence(self.data[key], mask)
 
         for key in self._structured_storage:
-            info._structured_storage[key] = info._array_backend.pack_padded_sequence(self._structured_storage[key], mask)
+            if mask is None:
+                info._structured_storage[key] = info._array_backend.flatten(self._structured_storage[key])
+            else:
+                info._structured_storage[key] = info._array_backend.pack_padded_sequence(self._structured_storage[key], mask)
 
         return info
         
@@ -135,8 +141,13 @@ def __add__(self, other):
         info._structured_storage = self._concatenate_dictionary(self._structured_storage, other._structured_storage, self._array_backend, other._array_backend)
         info.data = self._concatenate_dictionary(self.data, other.data, self._array_backend, other._array_backend)
 
-        info._key_mapping = self._key_mapping | other._key_mapping
-        info._shape_mapping = self._shape_mapping | other._shape_mapping
+        #combine key_mapping
+        info._key_mapping = self._key_mapping.copy()
+        info._key_mapping.update(other._key_mapping)
+
+        #combine shape_mapping
+        info._shape_mapping = self._shape_mapping.copy()
+        info._shape_mapping.update(other._shape_mapping)
         
         return info