Shortly: go to any JS/CSS/Scribunto source page (example), type anything, click on Show preview/changes - apparently no changes have been made. CodeEditor uses a different textarea box, so this won't work unless you switch to the standard editor mode (the upper-left corner button on the editor panel) and switch back again.
|Open||None||T41272 Bugs in "Live preview" feature (tracking)|
|Resolved||Fomafix||T78838 LivePreview: no changes reflected on preview/diff when using CodeEditor|
We already solved the underlying problem in MediaWiki core and CodeEditor by standardising on TextSelection API for retrieval of textarea content. This is already used by editWarning, and LivePreview should use it as well. That eliminates this problem.