Well, regardless of whether or not this is a real issue with using those two properties together, I have found a solution. For posterity's sake, here's what I did :

First, when building the anchor, I replaced ' ' with ' '
Code:
anchor.innerHTML = cfg['text'].replace(/ /g, " ");
I then removed the white-space attribute from my CSS. This was closer to a fix, but it still wasn't wrapping. On a flyer, I tried to put a space between the divs hoping that it would see the space and decide it was time to wrap.
Code:
//after building the div and appending it :
div.appendChild(document.createTextNode(' '));
That did the trick. And it works in both IE and FF. Now that this is finished, I can finish working on the "hard stuff".

Cheers!