MoveLayer not working in 10.1?

Am I imagining things or MoveLayer does not work in 10.1? I have the exact same code moving a layer in the TOC in 10.0 and it works fine, but in 10.1 I get an error saying “assert move_c is not None, ‘Did not find move layer.’ AssertionError: Did not find move layer.”
Has anyone seen this before?