> As a good citizen he wanted to file a documentation bug to have this behaviour documented. But R’s bug tracker seems not to be open to the public. So the story has to be recorded here for Google to find.

Huh? The bug tracker is here:

https://bugs.r-project.org/

Yes, for filing a bug you need to request an account because they apparently were overwhelmed with spam, as documented here:

https://www.r-project.org/bugs.html