CSS Media queries are not supported in IE8. Yes there are tricks to make them work, but in general it was not until IE9 that they became natively supported.

CSS3 @media Rule

So IE11 should certainly be able to handle them. However, I can infer what is happening in your case. Because you said you are using PRPC 6.x, that tells me you are likely using compatibility view in IE11 (otherwise PRPC 6.x will not even render properly). When you do this, you are kicking your user agent string back to an older IE version which does not natively support CSS media queries.