OK, quick explanation required for that.
Positions 1, 3 and 5 are as you'd expect: Bridge, both, neck. Completely normal tele wiring.
Position two is both pickups split (to opposite coils), but in series. Keeps it hum-cancelling and also keeps the volume similar to the other positions.
Position 4 is the same as position two with one difference: the neck coil runs in parallel with the 1nF capacitor. So it's like turning a tone control down on the neck pickup only. It's only subtly different to position 2 but it gets much more use - it has a very slight quack to it.
I'm considering doing something with position 2 as it doesn't get much use at the moment. Possibly a similar arrangement but with a resistor, or a different value of capacitor, or something.