MM Pets ignore knocked-down targets

I've recently been playing a new MM, a zombies/FF, and something that I've obviously noticed before, but just overlooked, finally clicked.

Scenario: My MM and his two un-upgraded zombie henchmen approach 2 even-conning minions. I instruct the zombies to attack 1 of the minions, and use force bolt to blast the other away. The zombies finish off the first minion about the time I force bolt the second, knocking it down and back.

BUG: The zombies will stand there, even if given a new instruction to close and attack, until the target starts rising to their feet. They will not close on, and engage, a target that is prone (i.e. knocked down).

I tested this with my Bots/FF MM, and even un-upgraded, they will engage using their distance attacks regardless of whether the target is knocked down or not, so this appears to be solely a hand-to-hand attack vs. knocked down target issue.

Regardless, this means that pets will not use certain attacks or engage, or even approach, knocked-down targets until they rise, thus negating much of the advantage of having a knock-down/knock-back attack in the first place.