Interesting, running just the number generation under node v6.5.0 gives:

     { '0': 340364, '1': 330093, '-1': 329543 }

So we see a slight bias for zero (elements are equal) there. ~Lemme try it in Chrome and get back to you.~

AHA, repro'd in Chrome latest: http://jsbin.com/cefuqi/edit?js,console

Also repros in node. Fascinating. There goes my afternoon...