sp_rename currently has a warning message that cannot be turned off. I would have expected SET ANSI_WARNINGS OFF to prevent this warning from appearing, but it does not:
"Caution: Changing any part of an object name could break scripts and stored procedures."
The reason this has been a problem for me is that it fills up all of the visibile history in the SQL Agent log, and makes any *real* error messages go out of scope (because only so many characters are held in the log).
I have worked around this by using a round-robin schema swap, but it makes deployments much more complicated, and affects performance, because the statistics go with the object when you move it to a different schema...