Google is seeing these as separate pages:
http://example.com/item:something.php
http://example.com/item%3Asomething.php
That pesky colon is the problem. In the browser url we see %3A, but
apache mod_rewrite automatically decodes it and sees it as ":" Since apache doesn't see the offending characters, we don't know how to use it here.
Any ideas on how to fix this?