So I just took the Unhindered perk to make light armor weigh nothing. I have a full set of Dark Brotherhood light armor on. The armor still weighs pounds. So I quit and reload and still the same thing. I remove all armor and equip again and still it's not weightless.

I've searched but can't find if this is a known bug. So...does the Unhindered perk not work on the Dark Brotherhood armor?

Look at ur carry weight not the stat on the piece of armor, that doesn't change, but ur carry weight should go down when u equip it

The armor's actual weight doesn't change. It'll still list a weight for each piece, right beside it's value, & DR.
But, it should no longer add to your encumbrance. As a matter of fact, if you're carrying more than one suit of the armor you're wearing, that shouldn't add to your weight either.