IIS returns null response when it can't find a default document and directory browsing is not installed

In IIS 7.5, when the “Directory Browsing” feature is installed in Windows 2008 R2 (but not enabled in the web.config file) then hitting directories without a default document will give a 403.14 error.  This is expected.

However, when the “Directory Browsing” feature is not installed, and you hit the same URL, IIS returns a 200 with a no response text.

http://localhost/css/

Content-Length    0
Date    Mon, 01 Apr 2013 12:31:16 GMT
Server    Microsoft-IIS/7.5

There doesn't seem to be a way to trap these errors and display a display a nice message.

This seems like a bug in IIS?  Anyone know how to trap this condition and show a custom 404 page?