Date.httpdate, rfc2822, and xmlschema mutate their arguments
ruby 2.0.0dev (2012-01-16 trunk 34316) [x86_64-darwin11.2.0]
2.0.0: UNKNOWN, 2.1: UNKNOWN, 2.2: UNKNOWN, 2.3: UNKNOWN
Date.httpdate, rfc2822, and xmlschema all mutate the string that is passed in.
I've attached a patch that fixes the problem along with tests that demonstrate the issue.