It should maintain its facing regardless of movement, otherwise it's pretty pointless. It should still automatically turn to fire at an enemy if it spots one, unless the tank is currently ordered to hold fire. Obviously this means the ability is effectively pointless for any tank that cannot hold fire, meaning that every tank would need that ability as well.
And every tank SHOULd have hold fire. Why the hell doesn't the Panther for God's sake? Relic has added hold-fire to vehicles then AT-guns in a piece-meal fashion just put it on all of them already dudes.