(Apologies for publicly posting a link into Cloudflare’s walled-garden, but archive.org comes up empty.)
The linked bug report shows that astonishing but deliberate regular expression treatment was reported 9 years ago. Still today I spent time trying to work out why my regular expression was not matching only to find that the dev hi-jacked the meaning of ^ and $ for another purpose. Man page still neglects to warn users.
Yeah, it does add some confusion. It should be documented, or maybe the use of ^ and $ should be explicitly refused except by special flag, or something.