User Atethnekos at en.wp reports:
"If in the source code there is <<nowwiki/>blockquote>, and in VE I select "<blockquote>" and delete it, when I save the <nowiki/> is left behind in the source code."
See https://en.wikipedia.org/w/index.php?title=User%3AThryduulf%2Fsandbox2&diff=565596201&oldid=565596137 for an example in by sandbox. Further testing shows that it also happens with other tags and even with plain text:
https://en.wikipedia.org/w/index.php?title=User%3AThryduulf%2Fsandbox2&diff=565596772&oldid=565596703
Version: unspecified
Severity: normal