Current SUMO software has no warning if more than one user is working on an article simultaneously -- or: SUMO doesn't warn a user who wants to edit an article while another user is editing it. Old SUMO software had this feature. This is a problem for l10n teams with several active users at the same time. German l10n team stumbled over that a couple of times.
Because of how we save article history, two contributors won't overwrite each others' work--though I do understand the frustration of two people duplicating the effort. As a work-around, maybe you could add a column to https://support.mozilla.com/de/kb/de-kitsune-updates/history to list who is working on what?
Hi James, we did this at the beginning. But we've realized that it's more work for us to add a comment for each edit we do than to "push our luck" and doing manually correction every weeks when this problem occurs. The article history is very helpful, indeed.