Skinning one of the Accordian Headers

[_tippedOver]

I'm trying to skin only one of the my headers in an accordion.

I'm using:
mainNav_ac["_header" + i].falseUpSkin = "HeaderSkinClosedFalse";
mainNav_ac["_header" + i].falseDownSkin = "HeaderSkinClosedFalse";
mainNav_ac["_header" + i].falseOverSkin = "HeaderSkinClosedFalse";
mainNav_ac["_header" + i].falseDisabledSkin = "HeaderSkinClosedFalse";
mainNav_ac["_header" + i].trueUpSkin = "HeaderSkinClosed";
mainNav_ac["_header" + i].trueDownSkin = "HeaderSkinClosed";
mainNav_ac["_header" + i].trueOverSkin = "HeaderSkinClosed";
mainNav_ac["_header" + i].trueDisabledSkin = "HeaderSkinClosed";

This works fine for everything except the "falseUpSkin" does anybody know why?

Cheers
_tippedOver