Brad,

I have a 3yr old XTC, and I've just started noticing this problem. I have discovered though, that it seems to happen more after significant climbing in a tree with smooth bark. I have ben climbing a pair of willow oaks on a reguar basis, and I tend to see a little slipping while in those trees. In a white oak or a yellow poplar I've yet to have the problem. Interesting thing is that I've always just let it go, after a few inches the knot seems to remember it's job and cinches down.

As far as the blake's configuration, I always use 4-2 with my XTC. 5-3 locks solid on that rope. On my sportline either works fine, but I'm so used to the 4-2 that I don't like to use the larger knot. Interestingly, my kids have difficulty advancing the hitch on the XTC, because it grabs so well, there is a paradox for ya!

Climb Safe! See ya between the trees!
Icabod