Deliberate mistake: When Jar Jar gets arrested in the Gungan city, in the second shot of Jar Jar and Obi-Wan, Obi-Wan and a part of the floor behind him are reversed. This can be seen, for example, because two of the red areas on the floor have switched positions, and Obi-Wan's braid and lightsaber are on the wrong side. (00:14:00)
Deliberate mistake: When Obi-Wan is fighting Darth Maul alone, after Obi-Wan cuts Maul's lightsaber in half, they start fighting on a different side of the pit. But after Maul kicks him, a close-up of Obi-Wan shows the wall and smoke of the area that they left. The shot has been reversed as well. The easiest way to see this is to watch his braid, which is on the wrong side. (01:56:55)
Chosen answer: According to "Inside the Worlds of Star Wars: Episode I" by Kristin Lund, they are "laser doors which lock into position in response to potentially lethal power outputs that occur intermittently during plasma activation process" (the fight takes place in a plasma energy processing plant). There are six laser doors in deference to an ancient Naboo legend in which Chaos is held back by six inpentrable gates. As you say though, they're really just a plot device to add dramatic tension to the duel!
Sierra1 ★