Stock ER4S cords do not exhibit this problem as the wiring is a thin two parallel conductor sheath instead of the round bundled one. It seems evident that the original 4S cord melds better with the junction point to the colored earpieces. Just looking at the colored earpiece strain relief, it works perfectly with the 4S cord...I remember seeing the 4P with the same strain relief, but with the singular thicker round cording that just didn't seem to be a perfect fit. As far as I'm concerned the reduced microphonics of the ER4P vs 4S is neglible to the point of being just plain false. From what I've gathered with Ety cord postings, the 4S cord is just seems to hold up better as I've read more posts about fraying or poorly fastened cord sheaths with the 4P more than with 4S.
But I also use the Fixup 4S cord instead, which although nothing truly special or exotic as far as the cording, does the job very well with as good construction you can expect from a lightweight portable and less microphonic cord. I prefer the Fixup cord as I wouldn't wince so much in terms of cost if the cord got damaged(the cost of a stock cord replacement costing much more than a cheap headphone)...unfortunately it is rumoured that Fixup cables aren't being produced anymore, so perhaps as far as availability goes I do need to be even more careful. But I'll still have the stock 4S cable to fall back on.
Given that I don't particularly like buying any portables with terribly weak jacks, or don't consider any Ety convenient or cheap enough to be throw around portable phones and there are really really great portable amps out there, I personally have no qualms going with the 4S version.