Is it just me or does “Puzzle box of Yog-Saron” always draw cards when the deck is empty?
I have yet to see this NOT happend to me…
It’s gona draw cards most of the time, you just gona remember the times it kills you 
A lot of spells have card draw.
When you case 10 random spells, it’s rather hard to NOT get any card draw.
As Ixnay says, you notice it more when you’re in fatigue. But if you actively start tracking, you’ll notice that it also often fills (or even overdraws) your hand when you are not in fatigue.