Thanks for noticing. The doc for ismethod() says:

  “Return true if the object is a bound method written in Python.”

and the docstring agrees with that:

  “Return true if the object is an instance method. [...]”

So the change isn't properly a regression when reading the docs. On the other hand, it's true that some code may rely on the previous behaviour, and the discrepancy between getmembers() and a manual test can be confusing.

By the way, Python 3 has ismethod() right:

>>> class B:
...   def f(self): pass
... 
>>> inspect.ismethod(B.f)
False
>>> inspect.ismethod(B().f)
True