Microsoft IIS caches all the style sheets that are placed inside the App_Themes folder, remembering the ones that are used by the web site pages (by all pages, not only the current one); the effect is easily visible looking at the HTML code sent to the client, noting that are included CSS links that were not specified for the page.
This behavior requires a strong attention on styles inheritance, but also can make Internet Explorer versions prior to the 9 to overflow the maximum number of style tags allowed: in these versions the maximum number of style tags is 32 and all the following ones are ignored.

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