Masonry IE9 showing a single column, always


My Masonry has only one column in ie9, always, though in Firefox it displays columns fine. I put a simple example in the Fiddle:

It's the same, with or without float:left. It seems to be the same no matter which of three imagesLoaded scripts I tried, and whether or not I have images:

So that leaves a problem in my Fiddle code? I tried applying the CSS elsewhere, I tried resetting IE settings to default, clearing IE cache, uploading my site so it's not on localhost, etc.

Any ideas? Thanks. :)

Thanks Jennifer,

I would just add that this problem/solution also applies to Metafizzy's Packery. I haven't tested Isotope but I wouldn't be surprised if you found it there as well.