Well, I think it's because it's attack not Attack ... <-- don't know if this can be the problem ^^
Well and now, when you play "attack" animation and then move the unit by mouse click, then the "attack" animation is gone and the unit play the "walk" animation.
If you play "attack" animation and you move the unit with triggers [SetUnitX() and SetUnitY()] then the unit still plays the "attack" animation