IV Troubles, Need Help

[wundrweapon]

I don't think I'm truly understanding this whole IV thing, so could someone please explain why this scenario occurs?
In the Day Care Annex on Omega Ruby, I have an Italian Ditto with all 6 IVs perfect. This Ditto is holding a Destiny Knot. I also have a Beldum with perfect IVs in all categories except for Speed, which isn't 0. This Beldum is holding an Everstone and has the Quiet nature.
After breeding multiple Beldum with this pair, I would theoretically get the following data at worst:

• Four perfect IVs
  
• Whatever the Beldum's speed is (not 0)
  
• Random IV for the fifth stat
  

After all, the Destiny Knot transfers five IVs to the offspring as chosen from each parent at random, right? Apparently not, because 50% of the Beldum I hatched have these stats:

• Non-perfect HP, SpD, Spe
  
• Perfect Att, Def, SpA
  

How the heck is this possible?! I'm so confused! Please help me understand this!!!