Last modified: 2013-08-28 00:23:42 UTC
See https://pl.wikipedia.org/w/index.php?title=Wojnicz&diff=37347163&oldid=37312891 for an example - I'm not sure what the problem is, here, since that's a meaningless tag :/.
Looks like it's what happens when you insert a reference without typing anything into the box. Hit "insert reference", leave the main field blank, go immediately to the insert button, and... https://pl.wikipedia.org/w/index.php?title=Wikipedysta%3AOkeyes_%28WMF%29&diff=37370424&oldid=37257359
Change 81438 had a related patch set uploaded by Esanders: Disable inserting/changing references when surface widget is empty https://gerrit.wikimedia.org/r/81438
Change 81438 merged by jenkins-bot: Disable inserting/changing references when surface widget is empty https://gerrit.wikimedia.org/r/81438
Fixed in master; will be deployed on Thursday as part of the regular push.