default.aspx is sometimes appended to the request URL, but sometimes not.

Hi,
I found a weird problem that, if a folder is access in the browser URL like //">http://<server>/<vdir>/, asp.net appends "default.aspx" to the URL when Request.URL is accessed (//default.aspx" mce_href="http://%3cserver%3e/%3Cvdir%3E/">http://<server>/<vdir>/default.aspx). However, in another IIS application, I found that asp.net won't append the "default.aspx" anymore.
In both IIS applications, the "default.aspx" file is there and set as the only "default document".
Anyone knows why there is such a difference? Thanks!
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