> First, it's clear from your statements that the Ctrl-[ code was
> previously intended to remove only the latest bookmark.

Um, no, let me clarify...not the latest - but the most recently visited.
(I started out saying most recently visited, but then only most recent, so sorry if that is what was confusing).

> However, hopefully I and Olivier have gained some measure of
> credibility over the years, which might cause you to wonder why I insist,
> and he then agreed, that ZTree has always been removing the bookmark of
> the currently highlighted directory, just as it says in the Help file.

I think this confusion is coming from assumption that we got to the the current directory using [/], thereby making it also the most recently visited
But obviously the current directory is not necessarily the most recently visited bookmark, and therein lies the issue.

> 6. Press F11 again to see which bookmark was removed.
> Voilà, D3 is gone. So it removed the current directory, not the
> most recent bookmark, from the list!

But I think you, and the documentation are inferring it was removing the current directory because it was the current directory - this is simply not true
The Ctrl-[ logic knew nothing about the current directory. All it knew is what was the most recently visited bookmark.
To be completely accurate it should have said:
"To remove the most recently visited directory (which may or may not be the current directory), from the list, press Ctrl-[." ;-)

This has gone unnoticed so long I guess because functionally Ctrl-[ is tied to the use of [/], so perhaps more often than not, Ctrl-[ is used when the most recently visited and current-directory are one in the same.
Obviously I wrote the function with [/] navigation in mind, so we never even discussed what should happen if the current directory was not the most recently visited bookmark.

Anyway, I think we can all agree the new behavior is more sensible, and now matches the (previously expected) documentation ;-)