Everbody know that you can switch weapon during fight, but before there was no potential need for caster to do that. Moreover i'm not sure that is intended that a weapon you switch back have an effet which remain after removing it. If you think about it you can see that is illogical, but it's probably right too that this is the game mechanic as well.
I'll stop bump that post if nobody else than me can see any ingame advantage to do it.