...sorry if my response came off as a little harsh there, orsal.

RL's been getting to me lately, and you and KO focusing on something that seemed so minor to me was a bit frustrating. I'll try to give a more reasonable explanation behind knowledge (arcana)...
For one, when I think of what classes primarily deal with undead, two come to mind: cleric and necromancer. Clerics have relatively little to do with undead than necromancers. Sure, clerics raise the dead and whatnot, but they don't interact with actual undead other than to turn/rebuke them. Necromancers, on the other hand, raise them, command them, and otherwise deal with undead-related issues. Not only that, but liches are also, in my experience, typically arcane in nature, rather than divine.
So while the SRD may say that knowledge of religion is related to undead, I really feel that its more arcana than religious in nature. So I went with arcana for purposes of learning undead abilities, rather than religion. Religion doesn't fit the theme of the class, nor does it adequately reflect the nature of undead, IMO. Religion may say that undead come from hell or the abyss, but arcana gives undead more definition. Clerics may be able to turn or rebuke undead, but wizards can really mess with them and focus exclusively on them, while clerics just have that ability as an additional feature.
If, as judges, you two would rather see it as knowledge (religion), I'll change it - like I said, it's not really that big of a point, and I'd rather see this approved than not over something small like that. But I'd rather keep it knowledge (arcana).