Serious UI flaw in IIS manager HTTP Redirects.
The HTTP Redirect feature is handy in IIS7+.
However, it does not work as expected when it comes to querystrings. This is crazy, but you can make it work by specifying an "exact" redir to www.some.com/$V$Q to preserve querystring over the 301.
Just need to remember this trick each time you want to make a redir.
Better explained here,