I reported this off of Phabricator months ago, and I know multiple WMF staff are aware of it, but this appears to be the first Phab listing. This issue is mentioned as a footnote in T112394. This appears to be a VE issue, which indirectly shows up in Flow. I had to clean up our United States article (!) after a VE user left these junk characters in the article. The characters are invisible in wikitext. They render as bizarre random arrows in VE. They create confusing inconsistencies between the edit view and rendered view, no matter which editor you're using. I know a number of people (including me) have run into a lot of bugs with Flow/VE copy-paste badly mangling content. I have no idea how many have been fixed, or even have Phabs open.

P.S. I did not deliberately set security to none. It seems to have been a side effect when I edited the title without touching the security field?? In any case I find it hard to imagine any security issues here.

Does not seem to be specific to Flow, so removing that tag.