We have updated the functionality of the Rogue quest reward Crystal Core in order to address some inconsistencies. This new functionality also applies to Dark Pharaoh Tekahn’s Battlecry effect.
Sounds like they tried to make it clear for new (or returning) players that it's not possible to dispel the buff with a silence. From that standpoint, it's pretty reasonable because some players might not understand that the thing that makes lackeys 4/4 was a hero aura, not a buff. And they would waste a silence trying to dispel it, AND they would think they silence didn't work because of a bug.
But, speaking of inconsistencies, they introduced quite a fwe with this change. First of all, cards don't do what their text says any more (contrary to what they say). So, the first card says that it adds or summons a 1/1 copy. Ok, that's it! When the minion is summoned, it is (and was) 1/1. Now the aura should take effect, which is 'your minions are 4/4', so the summoned 1/1 tokens should become 4/4s. Which they don't do anymore.
To put that into perspective, consider the interaction of Sonya Shadowdancer and Stonetusk Boar. The boar is already 1/1 that costs 1. So, Sonya basically gives you the copy of the original card. But it won't be affected be the Crystal Core aura. Which is pretty inconsistent because the first boar you summon becomes 4/4 but not any subsequent ones. But if you bounce and replay the boar, it will become 4/4. Weird, isn't it?
Also, the change is definitely a nerf to the rogue quest because the interaction with Charge minions is broken AND stolen minions remain 4/4 now. But it doesn't sound like they will be giving refunds.