It doesn't seem like holding an edit lock is required for a save, is
If user A edits first, then user B edits either after the lock times
out or forces the lock, whoever saves first will unknowingly lose
their changes when the second user saves- the changes will still be
in the history, but neither user will know that something has gone
This seems like a bug to me, but wanted to check first.
I've already created a feature request for optimistic locking which
if fixed would address this (http://jira.xwiki.org/jira/browse/ XWIKI-175), but maybe this should be patched in the meantime. Maybe
when the 2nd user saves we should redirect back to edit with the
first users changes in the text area, and a nice message explaining
that the 2nd user needs to merge their changes in, with their changes
presented elsewhere on the page for easy cut n paste.