As reported by @wowgetoffyourcellphone on the forums: units sometimes go ever so slightly too fast over an individual turn, making them quickly alternate between walking and running animation to disastrous effect.
The attached replay show this behaviour for blue cav at 3:15-30.
The source of this issue is that unitMotion is too optimistic about how much it can travel sometimes. This appears to be because the timeLeft computation rounds incorrectly. Changing the division arithmetic fixes it (though admittedly this is a tad slower).