Check origin point on the two animations/frames. If they're not the same (usually anchored on the feet) you'll get that. If it's an origin problem, the walk animation probably has the origin point at its knees instead of its feet.
To avoid this I usually set up all the animations, and then go to the first frame of each one, set origin and right click and use the "apply to all frames in animation". This kind of stuff is really annoying at first, but once you get the hang of it it's easy.