Yes, I have seen this before. I'm guessing you are using one of the "designer" litters that make our lives easier, but can be confusing for cats that have recently come in from the cold. Feral kittens only know dirt in the great outdoors as their litter box. When they are brought indoors, they need some help with the concept of using a litter box. Unfortunately, dirt is NOTHING LIKE pine pellets, sweat wheat, absorbent crystal pellets, recycled newspaper pellets, ground corn cob, etc., etc., .
The best thing to start them out with is the old-fashioned non-clumping clay litter. Once they are using it, gradually you can transition to the other types if you have one you prefer. I've never seen a litter of feral kittens that didn't use the clay litter as soon as it was offered to them. Toss a hand-ful of dirt from the garden on top of the clay litter if they still need convincing. This problem, like most we encounter with cats can be solved if we can get outside of our human frame of reference and imagine the world through the eyes of the cat. Easier said than done, right?
On the same subject with regard to older cats too, sometimes they will suddenly start to pee on a bed or couch for no apparent reason. Aside from the annoyance, this is actually a sign of affection. Cats that are alone a lot or unhappy with the kind of litter they are being offered will seek a place that smells like the person they miss or are fond of. Whereas in most cases cats will use the offending litter to defecate, they find couch, bedding or towels more suitable to urinate. I'm assuming they want to cover and will use anything to do that but with peeing since it disappears in cloth there is no need to cover. In one difficult case I took a small litter pan and put a hand towel inside as a last resort. The cat in question was very happy to pee on the towel and I just used a series of old thread bare towels until he just as mysteriously returned to the litter box and that was that. I never completely understood why he didn't use the litterbox for the 4 months it took. He stopped peeing on the couch and the bed and was faithful to the hand towel once I offered that option. There is an excellent brand of clay litter called "CAT ATTRACT" that is very effective to make cats happy with the litter box.
All of the variables need to be considered to solve why a cat does or doesn't do something. For example, declawed cats often have an aversion to walking on litter since it is either painful or unstable for them to walk on. Declawing removed the equivalent of what would be our fingertips at the first knuckle and this often makes cats look elsewhere than the litterbox to do their business.
All the best, Mike