get_normalized_parameters is appending duplicate non-oauth parameters to the returned value of this method causing the method signature check to fail.

So a call to this url http://example.com/v2/search/videos?oauth_nonce=79815175&oauth_timestamp=1295397962&oauth_consumer_key=mykey&oauth_signature_method=HMAC-SHA1&q=car&oauth_version=1.0&offset=10&oauth_signature=spWLI%2FGQjid7sQVd5%2FarahRxzJg%3D

will cause get_normalized_parameters() to return oauth_consumer_key=mykey&oauth_nonce=79815175&oauth_signature_method=HMAC-SHA1&oauth_timestamp=1295397962&oauth_version=1.0&offset=10&offset=10&q=car&q=car

notice the duplicate "offset" and "q" parameters.