Your pally is still assisting your new character, because the mob is hitting your pally (due to the blind being cast), not the new char, you get penalized. To make exp penalty go away, simply remove paladin from the equation. The assistance penalty is meant to penalize anyone who is using an outside party to level their character... In this case you are doing exactly that. Therefore, the tax on your exp is working just like it's supposed to.
Blinds, roots, stuns, heals, etc. may not do direct damage to the mob the lowbie is fighting, but they are still assisting the char in a way that the gm's are trying to prevent. The taunt skill doesn't seem to give the penalty, but thats just a lucky case of either unprogrammable situations or something the gm's chose just not to program in.
