[Quicksilver]

The pressure based switches are a bit failure prone. The way they fail is it takes more and more pressure to get them to turn on until they just don't work. Having the two switches in parallel is a good way to have redundancy to avoid a light failure plus as pointed out before: The brake system has redundant front and rear brake circuits so if one fails the brake lights should still come on.

The described situation where one switch does one rear light and the other switch controls the other side is either an error in testing or someone did a major hack job on the wiring harness.