Attack orders can be and looks like are pushed in front of formationwalk order.
That is generally also logic in single entity behaviour.
In case formation gets destroyed and then target dies, attacker is supposed to stop attacking target immediately.
That essentially leads to getting to old formationwalk command, what was not issue for packable units until rP24895, that introduced formationcompoennt into the order.
Hovewer abandoning this order without being in formation makes more sense. Probably this one and FormationLeave should be FORMATIONMEMBER specific commands and error out in INDIVIDUAL state, but thats too much refactoring and potential rabbit hole.