The interpretation I've heard is that a change of direction is considered a "stop".

Because if you're going one way, you have to "stop" going that way to go a different way.

Andy, I'll take this to it's logical extreme....what about a "loop"? A runner could turn all the way around back to 1B by running in a short circle without stopping, then proceed in the direction of 2B by curling the other way, again without stopping.

In this TWP situation, I'm going to judge an attempt to advance towards a particular base (and commitment to that base) when the runner is headed in that direction, but by rule if I run figure-eights all the way to 2B, have I ever stopped?? :D

Actually, I don't find that to be TWP-ish at all. Lots of runners make that little loop - probably not all the way to 2B, but in rounding the bag at first.

All this over an unnecessary rule :)

USA always had it pretty well spelled out (covering all the bases, as it were)...

turns right- committed to 1B
turns left & heads directly to 1B- committed to 1B.
turns left & heads directly to 2B- committed to 2B.
turns left & heads any direction except directly to 2B- committed to 1B.
(that's the one I think I see most often...)

And even there, the second and fourth clause are redundant. I teach it as
turns right- committed to 1B
turns left
- heads directly to 2B- committed to 2B.
- heads any direction except to 2B- committed to 1B.
I also clarify the difference between overrunning and rounding.