Totally normal. The string is stretching in and the serving is just slipping with it. You just need to get it reserved. I recomend that no slip serving. Its flat and overlaps so it doesnt seperate. Or, if u do it yourself, order some "synthetic senew", its the same as no slip just A HOLE LOT cheaper. You get a hole role of senew for like $7 compared to $119 for a small roll of the no slip stuff. The senew though, looks like its fraying, when infact its just little hairs, its no big deal. But, you do need to reserve it, no matter which way u decide, otherwise you will be replacing a cable very soon.