Pre-filling (e.g. https://www.mediawiki.org/wiki/User_talk:Mattflaschen-WMF?topiclist_preloadtitle=Preloaded%20title&topiclist_preload=User:Mattflaschen-WMF/Preloaded%20body%20example) is broken.
This is a regression. It loads for a flash, then disappears when the editor is initialized.
Originally reported by @Nirmos at https://www.mediawiki.org/wiki/Topic:Somjwnyml02q4db8 .
See https://phabricator.wikimedia.org/T59989#1500040 for more information.