They didn't film a scene a certain way to make people speculate on it. GL changed his mind later. All they had to change was the pre-fight talk & the new arrival of Anakin. Look closely at the saber hilt that Palpatine is using when he is dueling Mace. It's Anakin's. In the original scene Palpatine force grabbed Anakin's saber to fight the 4 masters trying to arrest him. This is the "real" reason why Palpatine still had a lightsaber left to fight Yoda. originally, that was the first time he pulled out his own saber. But when GL changed the story around, they reshot the arrest scene & had Palps snap out his saber from his sleeve there as well.
Sources? Making Of book & OS.