I checked a sequence where I copied the walk cycle and pasted it on into the animation chart.  I then checked the parameters and although the numbers are exactly the same, the legs are in a different position in each new past on.  I don't see how this is possible, but there it is.

If I click from the orginal frame to the new pasted on frame, the parameters are the same but the legs move, twisting slightly and not setting flat on the ground.  The next pasted cycle has even more distortion.  The hips and the top of the body, arms and all, stay in exactly the right postion, it's just the legs.

Since I can't use the walk cycle I added to the library due to the wandering foot problem and I have to make this robot walk into a room, it looks like I'm out of luck unless I want to tweek each cycle - a long, ugly process.  I end the spline at the end of each cycle.  I would think a copy and paste would give me exactly the same motion each time, but it doesn't.