Why does a Category 5 rated jack have different solder tail positions than a traditional jack?
CAT5 cabling, for some reason, doesn't use a simple 1:1 relationship between connector pin numbers and the wire colours and pairs.

CAT5 cables have 4 pairs of wires: Orange/Orange+white, Green/Green+white, Blue/Blue+white and Brown/Brown+white.  In CAT5 the colour pairs are assigned backwards (orange+white is 1, plain orange is 2), and the second pair (green) is split around the third pair (blue)*.

So from a CAT5 perspective the wires are numbered according to the second pinout, but from a connector perspective the pins are numbered as per the first pinout.

* Perhaps someone can clarify as to why this is - I have always wondered.