If you think about it, it is simulating properly. As the AC cycle passes from positive to negative (with respect to ground), the voltage across the lamp becomes 0 for a finite amount of time. It's the same in the real world but you don't notice it because the physical light bulb filament stays hot and continues to produce light during this transition. The bulb in MS doesn't experience the hysteresis effect so it blinks on and off when the applied voltage is at 0 VAC. If you slow the frequency of the AC source down and place a scope across the lamp, you can see the effect. The lamp is off, it then turns on with the filament gray, then as the voltage peaks, the filament turns red. Then the process reverse as it approaches 0 VAC then repeats for the negative cycle.
