Hello,
it has been reported at http://mail.python.org/pipermail/docs/2012-April/008215.html but given it raises some question whether it's a bug in the doc or in the code, i'd rather report the issue here and hear what other think:

>>>
In the Python 3.2.2 documentation (and earlier Python 3 versions), in
the Python/C API Reference Manual, chapter Object Implementation
Support, the documentation for PyMethodDef says:

  The ml_flags field is a bitfield which can include the following
  flags. The individual flags indicate either a calling convention or a
  binding convention. Of the calling convention flags, only METH_VARARGS
  and METH_KEYWORDS can be combined (but note that METH_KEYWORDS alone
  is equivalent to METH_VARARGS | METH_KEYWORDS).

The bit in the parenthetical is incorrect.  If you take a look at
PyCFunction_Call in Objects/methodobject.c, you will find a switch for
METH_VARARGS | METH_KEYWORDS, but no switch for METH_KEYWORDS.  Hence,
using METH_KEYWORDS will land you with a SystemError that complains
about METH_OLDARGS.

This is either a bug in the documentation, or a bug in Python.  In this
case, since the code has persisted through three major revisions of
Python 3, I suggest that the bug _is_ in the documentation (whether it
should be or not), since changing the code for this at this late date
means a programmer has to use METH_VARARGS | METH_KEYWORDS anyway for
compatibility.

It may be work pointing out specifically in the documentation that just
using METH_KEYWORDS will not work.
<<<

I think we can change PyCFunction_Call to accept METH_KEYWORDS as alias for METH_VARARGS | METH_KEYWORDS.
It cannot make incompatibility with existing code base.

I just ran into this too.

We should fix the code for 3.2 through 3.4, but change the docs for 3.2 and 3.3 to remove the parenthetical note.  For 3.4 we can leave the parenthetical note but say this is new in 3.4 (or maybe, that it doesn't actually work in some versions < 3.4).  I agree that for code to work consistently across all Python 3.2 and 3.3 microversions, extension code is going to have to include both flags anyway.