Hearthpwn

As Tomnov said. That's completely correct.

It's agreeably perhaps a bad design of sorts.
Though one thing to note is the use of the words "When you play" which is probably how they are coming to that decision, because the spells are cast effectively by the battlecry of the minion, not by you.
That said, you still take the Overload, which I suppose could be considered odd if nothing else.
Perhaps this is intended from a balance perspective then, since those spells contain overload costs to keep them in check. 

All that said, I totally agree that it's a little unfair that the spells don't proc the minion abilities.