I get two crashes on Windows with Python built in debug mode:

* I got a crash. I wasn't sure if it was an issue of incremental build, so I rebuilt Python.
* On a fresh build, Python crashed on the CALL_FUNCTION_KW opcode, when loading names, names was equal to 0xFFFFFFFFFFFFFFFF:

            names = POP();
            assert(PyTuple_Check(names)); <=== HERE

  Moreover, f->f_code was equal to 0xCBCBCBCBCBCBCBCB. But it was really weird. I added assertion to ensure that f->f_code was not equal 0xCBCBCBCBCBCBCBCB: the assertion didn't fail.

* I ran "git clean -fdx" and built again Python. This time, it went fine, moreover the whole test suite passed cleanly!? "== Tests result: SUCCESS ==" and "386 tests OK."

I build Python with:

   PCbuild\build.bat -d -p x64 -e