In some of the xx modules, a Py_mod_exec function steals a reference to the module argument when an error occurs (Py_XDECREF(m) after goto fail).  It's a bit pernicious given the modules' stated intent to be used as a template, although I'm not sure how often this has actually happened.  At the very least, I haven't noticed this outside the xx modules.

For Python <= 3.9, this affects xx_exec() in xxmodule.c and xx_modexec() in xxlimited.c.  For Python >= 3.10, this affects xx_exec() in xxmodule.c and xx_modexec() in xxlimited_35.c.