This is strange - the specificity of this rule is rather low and shouldn't be affecting the WP8 icon. I've tried adding it here and the icon was still working with it. This means that the real problem is probably somewhere else.
Maybe not the best solution but if you can't find it, you can use platform specific classes to avoid the issue, like this:
font: 1em/1em "awesome";
However you'll need to add this for every custom icon you have.
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