commit ca99f03151ecfa67a27591a0097dae9a890a6d75
Author: Gregory M. Turner <gmt@be-evil.net>
Date:   Wed Dec 3 00:26:12 2014 -0800

    types.py: correctly ignore virtual types
    
    During new_class and prepare_class, don't allow __instancecheck__ and
    __subclasscheck__ of putative metaclasses to influence the selection of
    the actual metaclass that is used, as not only is this behavior
    inconsistent with that of __build_class__, but with type_new.
    
    Signed-off-by: Gregory M. Turner <gmt@be-evil.net>

diff --git a/Lib/types.py b/Lib/types.py
index 7e4fec2..3022428 100644
--- a/Lib/types.py
+++ b/Lib/types.py
@@ -73,7 +73,7 @@ def prepare_class(name, bases=(), kwds=None):
             meta = type(bases[0])
         else:
             meta = type
-    if isinstance(meta, type):
+    if type.__instancecheck__(type, meta):
         # when meta is a type, we first determine the most-derived metaclass
         # instead of invoking the initial candidate directly
         meta = _calculate_meta(meta, bases)
@@ -88,9 +88,9 @@ def _calculate_meta(meta, bases):
     winner = meta
     for base in bases:
         base_meta = type(base)
-        if issubclass(winner, base_meta):
+        if type.__subclasscheck__(base_meta, winner):
             continue
-        if issubclass(base_meta, winner):
+        if type.__subclasscheck__(winner, base_meta):
             winner = base_meta
             continue
         # else: