If they always took the same route that's precisely because they have no experience yet, so the pathfinder can't "weighten" the returned paths. As a consequence, as long as the bots didn't notice that this path was dangerous for them, they will keep using the shortest path. Just wait for them with a grenade or two at hand to temperate their pretentions in this area and they should start to think again
Or perhaps what could be done is to lower the heuristic of the A* algorithm according to the age of the .pxp files...