For description of "backwards"--see the following link:
2009 Intermittent Wipers Backwards?
I suppose that when the interval selector is in the middle, the fact that it is backwards is not apparent. Supposedly, the switch operates correctly, it is just the markings on the stalk do not agree with the length of interval. Evidently, for pre-2009 Tacomas, this was not an issue. Today, I checked the intermittent wiper stalk on my 2005 Toyota Camry and it was fine with respect to markings and operation.