When you trade with the Timelords and get them to the max exp, they dont level up, instead, they lose the exp they gained
I'm using Regeneration 2.0.7 with forge version "36.2.2". I have installed "Atum, betterendforge, botania, curios, mekanism, mekanism generators, mekanism tools, mining dimension, patchouli, tropicraft and twilight forest" alongside regeneration mod.
Video evidence: https://youtu.be/fWErDxjs53Y

Considering this is the Weeping Angels Issue tracker, I think you're in the wrong place...
I have moved the issue to the correct repository now, please try and keep track of where you're posting issues...

As far as the actual issue goes, is xp important? I don't play Minecraft as much as I develop for it so I have no idea what Villagers do with it?

In villagers, it unlocks more trades, so if you didnt add trades for higher level timelords, i suppose this isnt a bug because there's no need for the levels
And for the issue tracker, i'm sorry i had trouble finding it