Quote - Leg-popping: I find that the knees will buckle in an animation which follows a walk path, but not in the same animation if the figure walks in place.  This suggests that the buckling may have something to do with how the Walk Designer is handling the legs when rotating the walking figure's body, rather than necessarily being flaws in the animated poses themselves.

Yes, the animated pose can be OK, as a pose, but not OK when used as a walk blend. I think that frame 15 (k 14 in the pose) usually seems to be a bad frame for knee bukle. Is it just a coincidence that this is exactly half way through the walk cycle?

The knee bukle seems to me to be one of the bigest problems, because we don't understand it properly. If we understood how and why it is happening, it might make a solution easier.

I think it is the IK solver trying to reconsile the distance between the foot and the hip by rotations of the shin and/or thigh, that is at the root of the problen. Setting limits on the twist and swing of the shin seems to go a long way towarsd resolving the problem, but is not without concequences for the feet, and perhaps other actors. A more elegant solution may be possible by adjusting the hip ytran in the pose, for problem fremes, but that is just a theory, I have not tested it. The 'hipHight' and 'thighLength' may also have a bearing on this. If the WD thinks the hip is higher or lower than it actually is, or that the thighs are longer or shorter that they actually are, that could contribute to the problem.

But all the above is just the idle rambelings of my mind, I may be completely on the wrong track.