Why is my bone broth creamy white?

[tankgirl73]

Okay, just as I've done many times before, I've been saving up my chicken bones in the freezer until I had enough to make a broth.  It's been boiling away for about 6 hours now, and the broth is... white.  Creamy, opaque, white.

I've never seen this before.  The only thing I can think of that I've done differently, is that more of these bones are from birds cooked in a pressure cooker, rather than roasted.  

I've been getting organic, free-range birds from a local farm, they come frozen, cut up half birds, about 3 lbs per each half.  I thaw them then pressure cook with a cup of water and sometimes some herbs for 12-13 minutes, I end up with juicy, yummy chicken meat ready for any recipe AND a good 2 cups worth of nearly 'instant' chicken broth.  

Once I've used the meat I store the bones.  Some of the bones were also from raw birds or roasted birds, but pretty sure that most were pressure cooked like this.  Would this change anything when it comes to making this stock now??