Switch 4 is different because it's a momentary.
They are all momentary. That different brown switch was probably a replacement by somebody...
Not to disregard the other switch replacements suggested, but I've used the $.30 yellow Omron switches suggested here when my line 6 pedals have started getting flaky (or were apart for any reason):
http://www.diystompboxes.com/smfforum/index.php?topic=36902.msg262021#msg262021They are built to be able to handle more pressure, and are a higher quality, more robust switch than L6 used, but will drop right into the PCB. You can cut the legs off the stock switches to help desoldering. The Omron's have worked flawlessly in the 3 or 4 of those pedals I've used them in.
Some people have suggested replacing the actuators with the ones from small bear, but I suspect they are identical. The most common problem with the stock ones (this from a L6 tech I spoke to) is them getting loose and pressing on the PCB switches crooked. Some lock tight on the nut might work or a lock washer (on the outside of the pedal, to keep the actuator spring to PC board spacing as designed).
Looks like someone else fixed the random patch problem by replacing the switches:
http://www.diystompboxes.com/smfforum/index.php?topic=51473.0Good luck!
The switch design seems cheesy but that type of tact switch is often rated 50,000 cycles or more.