Attempting to be brief as it’s off-topic (I just didn’t want to let the above go completely unanswered): Of the many, many things disputed in the world, the Dhammapada being in the Khuddhaka Nikāya is not one of them. However, only the Pali Dhammapada belongs to the Khuddhaka Nikāya and when you click on “Dhammapadas” you can see several more parallel texts exist (in Sanskrit, Gandhari, Ancient Chinese and so on) which, naturally, do not belong to the Pali Canon.
I don’t know what the reasoning was behind the “Dhammapadas” grouping in the sidemenu (maybe ask the powers that be in a split off thread if you want to follow-up on it), but I might guess that it was something like “well, they’ve got to go somewhere and this is an important and popular texts for which there are many parallels so it would be nice to group them together.” What I can certainly say is that, trying to get a grip on all this sprawl of texts confused and continues to confuse me; it’s part of the fun, right? 