I don't recall were I got this from (perhaps it was once explicitly in an employment agreement and I've assumed it was general) but I was under the impression that ALL employee's coding (at work or home and I am referring to employees, not contractors) is owned by the employer (or at least has first rights to it). This is why open source development on work or /own/ time is an issue.
-- Regards, Mark Hurd, B.Sc.(Ma.)(Hons.)