So I'm that guy who has had perpetual problems with his T5P cables. The first three shorted out and each died within a month. Then last March they replaced it with the updated cable, which lasted until about mid-December of last year, before the very same problem occurred. Obviously, I was displeased, so I wrote to Beyerdynamic's support—perhaps a little too pointed, but hey, I was annoyed. Since I live in Korea they coordinated with the local repair facility here to replace the entire headphones, box and all. (Huge kudos to Beyerdynamic support, by the way).
So now here I am with a new pair of T5Ps, and they feel almost nothing like the old pair! The clamp is much, MUCH tighter (in a good way), the adjustable notches are firm and maintain their setting, the entire construction is really solid, something my fiancee noted ("Are those even the same model?" she asked). This leads me to believe that I must've gotten a lemon, or that there was a production issue with a few of the earlier models (the serial numbers are 7,000+ apart). The T5Ps I'm now using feel much better engineered than the ones I bought in December of 2013.
Honestly, I had begun to write these headphones off due to my frustrations with the cable & build quality. I even bought a pair of Shure SE846s and have been using them. However listening to these new T5Ps is like visiting an old friend, or settling into a nice, comfy chair. I'm glad I didn't write them off completely.