It will result in a 404. I've found if no colon is present, no 404 occurs. So I'm guessing the colon is causing wordpress to fallover?
If an ampersand "&" is present in the url for an argument e.g. session expired you will get the 404 page as well.
I do not code, but wondering if someone here more knowledge knows which php file(s) and what code I need to use?
From researching "clean_url" may need to be used so the url used doesn't call WP to fall over?