Is IIS performing an illegal character substitution? If so, how to stop it?

Question

Context: ASP.NET MVC running in IIS, with a a UTF-8 %-encoded URL.

Using the standard project template, and a test-action in HomeController like:

<

Answer 1

Ultimately, to get around this, I had to use request.ServerVariables["HTTP_URL"] and some manual parsing, with a bunch of error-handling fallbacks (additionally compensating for some related glitches in Uri). Not great, but only affects a tiny minority of awkward requests.