It's normal. No synchros in reverse, which means the car must be stopped completely and the input shaft must come to a complete stop in order for the tranny to be shifted into reverse. But occasionally the input shaft is still spinning from inertia. Try waiting a couple of seconds after pressing the clutch pedal, de-clutch and re-clutch, or shift into first at a complete standstill then reverse.
I think every car is a little different in this regard. My Protege will let me shift from neutral to reverse every time without complaint, while the 5 occasionally balks and requires declutching and clutching. On the other hand, my old '88 Accord usually refused to go into reverse without grinding unless you did the first-reverse trick.
