nth-child and media query breaks system

[jklue]

Thanks for the awesome framework. I'm having an issue where only the first class with an nth-child() selector is compiled into the final css stylesheet, when there are 2 or more elements with nth-child() and the same csswizardy grid class.

This code:

.core-product:nth-child(1), .core-product:nth-child(2) {
    @extend %desk--two-thirds;
}

.. results in only the first mentioned class:nth-child getting the property-value pair in the resultant .css:

.core-product:nth-child(1){
    width: 66.666%; 
}

Am I doing something wrong? Thanks.