Terry -

I don't furl leaders from Uni nor mono, but the ones I furl from Danville 210 Flymaster Plus fly tying thread do something similar, but not as dramatically as you are describing. Not sure exactly why they do that, but it seems that the stretching "unfurls" them and the quick release doesn't let them regain their furl in an orderly or neat way, but produces those tangles.

Typically, it is a matter of "unwinding" them, just letting the furl relax back to what it was before you applied a lot of tension to the leader and releasing that tension quickly. Work from the tip end and help the tippet and leader unwind.

You're not doing anything wrong, unless you consider sticking a fly in a bush once in a while wrong.

John