This seems more prevalent for female characters from my PoV than it is for males. It also seems to vary in severity from one to the next.
What's going on is that the feet tend to clip through the lower leg of the character slightly when jogging. When running/sprinting the foot clips through the leg higher up sometimes a little and sometimes a lot (to the point that it would make you think they'd trip on their own feet smacking into the back of their legs a little below the knee).
For males this effect is less pronounced but it is till there if you're paying attention. The clipping is usually less visible.
I made a quick set of recordings to display the clipping issue. Follow the mouse and there it is. Its hard to see at first due to the way youtube adjusted the video into such a small screen (and my client was using an old windows mode resolution which made it worse). By the time the purple KDF alien shows up it gets a little easier to see and when the Ferasan is shown, the clipping is blatantly visible. Once the Reman shows up, the clipping returns to being hard to see.
http://www.youtube.com/watch?v=YimgvEie7DY