MVC .NET Urls aren't routed using the RouteCollection

We're using MVC .NET and the RouteCollection class to route URLs in our web app. This func开发者_如何学Ctions normally until we pass a URL containing the the text "PRN" anywhere inside the URL. When this happens, the routing will not occur and a 400 Page Not Found error is returned to the client. It's like something is throwing the error before the routing collection is even consulted, because the route the URL should take is never touched (by that I mean the underlying code's break-point is never hit, though the exact same URL without the string "PRN" will hit the break-point).

So I thought it might be a page validation issue, that maybe Microsoft decided to throw exceptions when the URL contains the phrase "PRN" because it is like "print" or "porn" but if that were the case then we'd see the "A potentially dangerous Request.Form value was detected from the client" error, but we don't.

Researching this has been a hassle because Google thinks PRN should return results for "porn", which means 98% of my search results are invalid (and inappropriate). Using the "-porn" clause in Google drops your results down to about 10-30 hits, all useless.

Does anyone know why a URL containing the string "PRN" will not route properly? If you have any posts or threads to point me to, that would be awesome (again, Google has failed me).