Asp.net 4.0 custom provider

I used the custom disk output caching provider provided at this url http://weblogs.asp.net/gunnarpeipman/archive/2009/11/19/asp-net-4-0-writing-custom-output-cache-providers.aspx.
When ran the project it created two files. When I refreshed the page it cached the css files as well. Why didn't it cache it the first time?

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