We give a direct combinatorial proof of the $q,t$-symmetry relation $\tilde H_μ(X;q,t)=\tilde H_{μ'}(X;t,q)$ in the Macdonald polynomials $\tilde H_μ$ at the specialization $q=1$. The bijection demonstrates that the Macdonald inv statistic on the permutations of any given row of a Young diagram filling is Mahonian. Moreover, our bijection gives rise a family of new bijections on words that preserves the classical Mahonian inv statistic.