It's not only the pursuers that scatter all over the place, the pursued do too.
I've had several incidents post-patch where a routing unit has left the field yet the pursuers are still trying to get at them, the reason being that an individual of that unit is still on the field and a considerable distance away too, - on one occasion stuck behind a ladder - but he doesn't have a banner or marker on the radar to show he's there, and with this seasons relatively drab outfits he's rather difficult to spot.
Oddly one routing unit came back on the pitch and only when I killed them all did a banner pop up above the individual, about 400m away. May be a partial explanation for the behavior of some pursuers. I remember having similar trouble with stray individuals after installing DarthMod in RTW.