>>> class a1: pass
... 
>>> a2 = type('a2', (), {})
>>> class a3(object): pass
... 
>>> a1
<class __main__.a1 at 0x815111c>
>>> a2
<class '__main__.a2'>
>>> a3
<class '__main__.a3'>
>>> import new
>>> new.instance(a1)
<__main__.a1 instance at 0x8148a04>
>>> new.instance(a2)
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
TypeError: instance() argument 1 must be class, not type
>>> new.instance(a3)
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
TypeError: instance() argument 1 must be class, not type

2.2 branch and current CVS...  _so_ not a 2.2 bugfix
necessity, tho :)