App_Offline.htm with IIS 7.0 - problem

Hi, I have problem with App_Offline.htm in web application under IIS 7.0.

Firefox and Opera (IE show as html) show only text because server send to the browser this headers:

HTTP/1.0 404 Not Found
Server: Microsoft-IIS/7.0
X-Powered-By: ASP.NET
Content-Length: 1641
Content-Type: text/plain

It is bug of IIS 7.0??? Because IIS 5.1 and IIS 6.0 send Content-Type: text/html...
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