The old version was

 243 __inline static void _cond_signal(COND_T  *cond) {	
 244     /* NOTE: This must be called with the mutex held */	
 245     if (cond->n_waiting > 0) {	
 246         if (!ReleaseSemaphore(cond->sem, 1, NULL))	
 247             Py_FatalError("ReleaseSemaphore() failed");	
 248         --cond->n_waiting;	
 249     }	
 250 }	

So the test should be "if (cv->waiting > 0)" not "if (cv->waiting)".