It happened to me a couple of times today, but I dismissed it as an error of mine. While looking at recent changes, i saw it happened some more times to different users.
When one edits a section of a long article, upon saving the page a big portion of the article (sometimes everything from that section down to the end) gets replicated, and you end up with an article twice as long.
Saw it also on it:Wikipedia:Bar, the equivalent of the english Village Pump. Went from 120 KB to 240 KB in a single edit that inserted an entire copy of the Bar inside a comment.
See for example this edit (image maintenance page):
http://it.wikipedia.org/w/wiki.phtml?title=Wikipedia:Immagini_da_verificare&...
User:Painlord2k was just trying to remove the [[:Image:Torvalds1.jpg]] at the end, but the entire 134-items list in the previous section was duplicated, and the article got twice as long!
Alfio