User blog comment:Dopp/Technical Update: November 29, 2011/@comment-1331296-20111202182242/@comment-1997905-20111202184013

The start timestamp is part of the edit form HTML, and is submitted both times you click edit. MediaWiki sees the revision of the page as having your signature on it (no tildes), whereas the newly submitted revision doesn't. Since both submissions share the same timestamp and both technically modify the same lines, it generates a conflict. It's possible to do without the RTE, but as you said, it's more difficult.