I don't know if it matters, but I'm not doing it with a "Submit" button; I'm doing it by a link, i.e., one page lists the records, and if you click on one of them, it passes the record i.d. in the URL and goes to a page that finds that record and then performs the set fields and commit on the found record.
If someone's in the record, it returns "Error: 301 - Record is in use by another user."