"If you take either end of a furled mono leader in each hand and give it a pull, you'll feel how elastic it is. It almost feels like a rubber band. When you put it under full tension, and suddenly release (like when you pull free from a snag), it's that slingshot effect that causes everything to end up in a mess. So if you tend to get snagged alot, that elasticity can be a problem."
What "pszy22" has stated is the reason and what I do when that happens is just cast the furled leader out on the moving water and let the moving water "drag" the tangles out. Seems to work everytime for me. I do not use any thread leaders because I do like the "stretch" that mono or flurorcarbon provides. Before giving up on mono or flurorcarbon furled leaders, give casting them into the current a try.
Just my 1/2 cent opinion...
Warren
Fly fishing and fly tying are two things that I do, and when I am doing them, they are the only 2 things I think about. They clear my mind.