When her pet was tanking, she didn't see a change. That seems obvious-- if the pet holds the highest aggro, it would be pointless for them to run around in circles to try and get behind a mob. Unless the target was somehow stunned (Rogues use that tactic all the time, of course), but she didn't say that she was able to test that case at all.
But when she or someone else was tanking, sure enough, the pet slowly circled around to the side of the enemy (which, I believe counts as "the back" in terms of theorycrafting), and attacked there. The problem was that the pet did move slowly, and during the whole time spent positioning, wasn't attacking at all.
It sounds like Blizzard is trying to get some complicated code down here, and I wonder if the result is really worth the effort. But then again, for Hunters who raid, a buff to their pet's attack like this is probably very welcome. And the real reason for this change probably has nothing to do with attacking from behind anyway-- despite the short loss of DPS, keeping pets out of frontal AoE and cleave attacks is definitely a terrific benefit.