[Jerhal]

You end up being better off using two weapons that are the same, instead of using a lighter smaller weapon for your off-hand. Once you get Weapon Focus and Weapon Specialization the bonus' they give more then make up for the penalties of using two weapons of the same kind. Unless you spend 2 more feats on your smaller weapon (which is a waste) you actually have a lower to hit value with the smaller weapon.

It also seems you can't dual wield light flails. The light flail always needs to be in the main hand for some reason. Although you can pair it up with a mace or hammer in the off hand.