I would say this is STILL a “problem”… And one you want to avoid at all costs. It happens much sooner on the rear shifter than the front, generally, which is logical because of the difference in how often they are used. I’ve run the front cable well over double the miles as the rear cable, and still haven’t seen the fraying issue, which is usually visible if you look closely into where the cable begins in the shifter. Pull back the hood cover and shift through the gears, inspecting all that is visible of the cable, and you may see it beginning to happen, individual wires already breaking.
I BARELY escaped the nasty situation Saddlesaur mentioned, when my rear cable broke inside the shifters. I had already ignored the EARLY WARNING that this is happening: the rear derailleur stops shifting cleanly and needs some adjustment at the barrel adjuster, and this is to get MORE tension on the cable. That’s because with many individual wires on the cable already broken inside your shifter mech, the cable really DOES STRETCH. So you have to use the barrel adjuster to dial it in again, and that’s when you BETTER CHANGE CABLES NOW!
I didn’t heed my own advice… I thought I’d tweaked a derailleur out of true somehow, and missed the warning signal!
I was fortunate that with some time-consuming and careful work I was able to get the frayed wire back out of the shifter without having to resort to a lot of digging bits of broken wires out too. That can cost you a small bundle of cash if the shop has to do that for you because you let the cable break. I do almost ALL bike maintenance myself on my bikes because I can and because it’s a hassle to drive an hour away and leave my bike and return another day, but my shop advises changing the cables by 2500 miles to avoid that very issue. (I always get much more than that before changing, but I’d pushed it too far this time when mine broke, close to 4500 miles.) And on this particular occasion, I had just recently done an inspection inside the shifter trying to see if there was any fraying, and I saw none and thought I was okay. However, the fraying happened about 3/4" up from the endpoint of the cable and I could NOT see it happening.
My best advice is PAY ATTENTION TO EARLY WARNINGS! When either derailleur seems to get out of adjustment, it MAY be because the cable is already fraying somewhere.
I use standard Shimano stainless steel cables. They are quality made, can often be found in bulk at very reasonable price, and slide will inside housings. And it is SO EASY to change a cable before it breaks. Yes, a little fiddling to dial everything in but pretty minor, really.
One other thought, aimed at bike manufacturers, PLEASE DESIGN BIKES FOR FULL CABLE HOUSINGS, especially if cables are INTERNAL! I’m not a big fan of internal with PARTIAL HOUSINGS, but with FULL HOUSINGS, it is a GREAT IMPROVEMENT. Almost nowhere for corrosive elements to intrude, cables are protected from wear and make cleaning the exterior of the bike so much easier, and yeah, the aerodynamics of the bike are improved too.
When I made the first cable change on my DOMANE, I was braced for some fun, expecting to have to fiddle with routing the cable through the frame and all that potentially entails. I looked inside the handy storage area in the downtube, accessed by removing the little door that holds the water bottle cage, and realized the cable housings (and disc brake hose) were complete all the way through the bike! HAH! A simple process of cleanly cutting the cable free at the derailleur and then pull it back up out at the shifter, and then push the new cable in! It was absolute joy!
I’m still running the original housings, with nearly 23,000 miles on the bike. It will take a little bit of fiddling when I have to change them out, but they are still smooth. I’m on the about the 6th rear cable, and the changes have been so easy! I can handle the fiddling required, knowing it’ll give me another 4 years of easy cable changes once it’s done.