eshell bug? extra TAB after prompt

[Rainer J.H. Brandt]

Hi,

eshell often, but not always, prints an extra TAB immediately after the
prompt.  I have

  (setq eshell-prompt-regexp "$ "
    eshell-prompt-function (lambda nil "$ "))

but the problem is reproducible under "emacs -q".

I use Emacs 27.1 under Ubuntu, but I've seen the problem on other
installations, too.

It often happens when the last word of the command was the result of
completion, but I've seen exceptions to this rule.

Is it a bug?  (I couldn't find anything related to such a problem.)
Or am I overlooking something?

BTW:  Is this the right place for questions about eshell?

Thanks,
Rainer J.H. Brandt