A Close Order unit in which the majority of models have this special rule is considered to be in Combat Order rather than Marching Column even if it is deeper than it is wide, provided it contains enough models per rank to claim a rank bonus. Whilst such a unit is deeper than it is wide it can claim a rank bonus and can perform a charge move, but cannot march at triple its Movement characteristic. In addition, should such a unit be charged by an enemy unit with the First Charge special rule, it does not become Disrupted.
If a unit with this special rule wishes to adopt Marching Column and march at triple its Movement characteristic, it must be deeper than it is wide and contain fewer models per rank than it requires to claim a rank bonus.