Flies that spin can make an absolutely awful mess of your leader, particularly if you are fishing multiple flies. All you need is one "spinner" in the group and all your flies join together in an unhappy marriage of steel, feathers and leader material. Old-style, duck-wing wet flies have always been the worst offender for me. Strangely enough I've also had a similar problem with pheasant-tail nymphs. This worst part is that I know I'm to blame for the problem because I've tied something off center or out of balance. 8T