IE9 Stylesheet Not Loading Due to Case Sensitivity

I recently discovered something very dastardly about IE9 (and possibly other versions – I haven’t tested them all): class names are case sensitive in IE9. In other words, if your HTML looks something like this:

...
<div class = "MyDiv"></div>
...

And your CSS looks something like this:

.myDiv {
/* Styles Here */
}

Internet Explorer will not apply the styles to the div because MyDiv is not the same as myDiv. However, if you were to run this HTML through another browser, the page will render as expected.

Oh, and why the weird post title? Well, it appears that IE9 not properly loading stylesheets is a common problem. However, it usually has to do with the mime type of the CSS file and less to do with the problem discussed here. I wanted to draw attention to the main symptom so that someone else who got as frustrated as I did might find the answer sooner.