How do I describe this? Clip two biners on a Dynex/Dyneema sling, push one biner through the other and clip the loop of two with that biner. You now have an extendable quickdraw. Choose to extend or not by using the draw as is, or by clipping your gear and then unclipping the second biner from all but one strand. Voila, nice for keeping rope drag under control and save some weight on biners.

Not quite sure what to call this method.

My question came about when I was cleaning a route and my buddy pointed out that several of my draws are "back-clipped". Turns out that since a Dynex sling is a lot less stiff than a sport quick draw, the rope side biner twist around resulting an a "back-clip".

Is this an issue at all? Is there a change of the rope unclipping on a fall? What method do you use to extend.

_________________
You may still be here tomorrow, but your dreams may not. Cat Stevens

Nah, you'll be fine. I think it's only a realistic problem with short and stiff slings.

Although it doesn't happen often a friend of mine actually witnessed the dreaded 'back clip unclip'. A guy was climbing the route 'Blaze of Glory' at Silvermine and after back-clipping the final bolt he headed towards the chains. He fell above the bolt, the rope ran over the gate, the gate opened and released the rope from its clutches. No injury resulted just a whipper but it could have been worse.

Rather clip the standard way I'd say

as per shorti's comment, the risk of back-clip-unclipping is miniscule with a long & supple sling. sport draws with a stiff dogbone is more risky, as per cricket's story.

As far as I know, this technique of making an extendable quickdraw is called a "Yosemite draw" - but hey, we don't have to let the Americans claim that one...
It is quite easy to set this up wrong and end up with an "extendable draw" that just falls apart when you try extend it, so if you do not know how to do this then it would probably be best to get someone to show you before you try it.