Nice catch!. That's due to the insufficient arch in the back. It should be more "bow" like if you know what I mean, that way the legs in front of the body effect wouldn't be as strong as it is.
Anyways, I promised to share, so here is what I found out after the second course of my animation journey:
A walk cycle is easy.
An average/decent looking walk cycle is difficult as hell.
There are 5 crucial positions in every walk cycle (the 6th being the first one repeated and reversed)
The frames (usually) for the steps are as follows: 1, 4, 7, 10, 13 and then 16 for the inverted first step.
You absolutely must remember how the shoulder line and the pelvis tend to oppose each other:
Don't forget about rotating the feet on the Z axis slightly (so that they are facing away from each other).
Obviously a lot more went into this one but these were things that I didn't focus too much attention on.
I hope it helps