Just stumbled upon these leaked variables: x, y, line, breakLine. Putting them in local scope shouldn't break anything :)

function Group:Layout ()
    self.limit = self:GetLimit()
    x, y = 0, 0
    line = 0

    function breakLine()
        y = y + line
        line, x = 0, 0
    end

Oh... my... O.o
Nice catch! Can't believe I forgot to make them local...

Fixed