Sorry, I've missed your update=)
Perhaps if you want to keep this frame its up to you, its not really that critical, though usually an even number of frames for a walk is an easier way to divide steps for both sides.
Tweening goes between two points, and no matter how many frames you using its usually even amount between right and left cycle. Same goes for any direction. Again, not necessarily.=)
About update, i think bending leg before it move forward would benefit a piece.=) Now knee goes up (back) with a feet and return down (forward) with a feet as well. If leg is actually bends knee would go down (forward) first while feet remains on a back and then feet would catch up with a rest.
Great work anyway.