Dideved - 2:32 pm on May 12, 2013 (gmt 0)
Turns out this has nothing to do with your rewrite rules. Apache for Windows intentionally disallows colons in the first path segment. It's meant to avoid security issues, since the underlying filesystem also uses colons.
See https://issues.apache.org/bugzilla/show_bug.cgi?id=41441 for more into.