I'm guessing you're using Independent angle on the feet to keep them looking 'planted'? If so, that's a completely valid technique, however, it does mess up bone flipping with IK. The reason is that bone flipping doesn't mirror the foot bone when using Independent Angle.
To work around this, you'll need to keyframe the foot bone's rotation just before the flip, and then rotate the bone to the proper angle after the flip. It's a little annoying but not too much trouble.
Tip: you can make the flip look smoother by scaling the foot bone 'shorter' during the 'turn', and then scaling it back to full length after the turn. This creates the illusion of foreshortening. You only need this for one or two frames. It's a subtle effect but your brain will sense it as smoother animation. If you want to take it another step, use the foot bone's rotation to slightly angle the foot down during the 'turn'. This can help make the foot look like it has some depth.
Here's a quick example:
You might also have noticed that the leg straightens slightly in the turn. This not only gives the animation a little more life, it helps the foreshortening effect as the knee 'points' to camera.
I'd like to add that, while it's technically possible to put all this inside a Smart Bone Action, I don't recommend that because you'll be giving up some freedom with the rig. It's up to you though.