The DC-4 problems referred to were the result of a generally underdesigned elevator hinge arrangement, and were solved by redesign.
On the DC-6, this also, oddly enough, re-appeared, and the 'fix' was to add an additional elevator hinge at the extreme tip, to aleveate unwanted vibrartion, which manifested itself as a rather unpleasant control surface flutter at Vne.
The DC4, DC6 and the DC7 shared the same wing planform (with minor variations, mostly washout toward the tip) but had entirely different tail surface arrangements, with regard to Reynolds number.