The (prev) links rely on having a &back= id from which they can be filled. This works neatly if you want to go back one level, but try and go back two in a row and the whole thing falls apart.
For example:, take https://en.wikipedia.org/w/index.php?title=Special:WhatLinksHere/Abacus . Now go forward (next) two times, and then back twice. In fact, you get trapped on page 2, because now there's no &back= id to use in the generation of a (prev) link.
WLH should probably copy other special pages and do "(prev)" using a dir=prev parameter.