I run reflinks.py witch use
(every script that use this are potentially affected by this bug).
After the script retrieve the content of the page, and before the script save the page, a user made an edit at the page. The script save the page with the old content without any warning.
In this way, if a user made an edit in the meantime the script is running, this will be lost.
Example: https://it.wikipedia.org/w/index.php?title=Lituania&diff=prev&oldid=75880159 where my bot undo the anonymous user edit