%09 in a URL causes IIS (HTTP.SYS?) to return HTTP 400 immediately

Question

I've discovered that IIS7, 7.5 and 8 (and probably previous versions too) will fail-fast when encountering any URL that contains %09 that is not part of a querystring.

StackOverflow itself exhibits the same behavior, observe:

http://www.stackoverflow.com/questions/%09

This is annoying for my application because I have built a web-service which should return text/xml for every request, even invalid ones, containing a specific XML document format containing error codes. I've found that some webservice clients pass the %09 (often caused by a user copying and pasting) to my service, but my server returns an ugly HTML response that seems hard-coded into HTTP.SYS (I overrode the HTTP 400 error response in IIS, but it has no effect).

Bad Request - Invalid URL

HTTP Error 400. The request URL is invalid.

Is there any workaround or solution for this?

Memorandum:

For comparison:

• Google serves a HTTP 404 correctly: https://www.google.com/%09
• Apache seems to let MediaWiki handle the error: http://en.wikipedia.org/wiki/Foo%09
• IIS doesn't: http://microsoft.com/download/%09