The rule in the subject seems rather strange or pointless to me. In the example they give in the BRB an unit of HE archers declare three different charge reactions to three different charges they face. But since it is the person declaring the charges that chooses the order in which the charging units move it will only play to the charges advantage. If they want the HE unit to flee they will charge first with the unit where this charge reaction was chosen. If they want combat they will charge first with the unit where the charge reaction was hold. In any case they will never stand and shoot since they cannot stand and shoot if they are fleeing nor if they are tied up in close combat.
Also, if they first charge with the unit so that the HE unit flee, will the two other charges cause the HE unit to flee twice more, even though they had chosen different charge reactions towards them, making them a grand total of 6D6 inches flee movement? Or if the first flee movement takes the HE unit out of possible charge range, will they not flee again since the charge cannot be completed? I cannot find in the BRB anything about that a unit only can flee once.
Maybe not so clearly explained, hope you understand anyway.