Steps to reproduce:
- select and copy multiline text from Terminal on macOS 10.13.6
- in Chrome 68.0.3440.84, open a page on mediawiki.org such as https://www.mediawiki.org/wiki/Extension:TimedMediaHandler/VP9_transition/reports with the new wikitext editor enabled
- click 'edit source'
- the text should paste exactly as originally, with one newline per line
- every line has a blank line between it and the next line
- use "paste and match style" instead: