Slitherine

I charged a light foot that was two hexes from map edge, it evaded and quite generously stopped at the map edge and got hit in rear, took a cohesion drop, then continued to evade off the map

This is not a bug.

A BG can evade and stop right at the edge of the map, then get hit, have its cohesion dropped to routing and then rout off-the-map.