This is because it uses the same mechanics to prevent actions as Supernova does. It does not allow absolutely anything. Compare it to Berserker's Call, Winter's Curse And Duel: You can give orders during those 3 and they are getting executed as soon as they expire. Meanwhile, you aren't even allowed to order anything for something to get queued up and done after the roar expires. This also includes stuff which ignores disables (Morphling's Morph, Abaddon's Borrowed Time and Ursa's aghs upgraded Enrage), as well as preventing affected units from attacking Axe when he Berserker's Calls, or their allies during Winter's Curse.

Instead of using that "can't act" mechanic, it should rather be like Berserker's Call, where periodic attack (in this case move) orders prevent the unit from doing anything.