>>>>> Bug reports for GNU Emacs, the Swiss army knife of text editors <Michael> writes:

    > Hi Colin, could you please post another screenshot that shows the
    > situation directly after executing your recipe?  It seems in the
    > screenshot you had posted the window that displayed the
    > completions was selected.

    > Did you select the window?  If yes: please provide a screenshot
    > where the state of Emacs has not been altered by any subsequent
    > user actions.  Even a (very small!) animated gif could be helpful
    > (or a link to one).

I attach the screenshots.

I notice that neither the mouse pointer nor the filled-block cursor are
visible in the pictures. Therefore I'll indicate where these items are,
as we traverse the steps below. The words 'visible', 'non-visible' will
refer only to the pictures, of course.

1. emacs -Q <RET>

2. I take pic00.png. The non-visible, filled-block cursor is present in
the window. I have not moved the mouse so there is no mouse pointer, and
this remains the case until Step 7.

3. C-h f completions

4. I take pic01.png. The non-visible, filled-block cursor is to the
right of the word 'completion' in the 'Describe Function' window. A
visible, open-block cursor is in the scratch buffer.

5. <TAB>

6. I take pic02.png. A visible, open-block cursor has appeared in the
completions buffer, enclosing the letter C in the word 'Click'. The
visible, open-block cursor remains in the scratch buffer, and the
non-visible, filled-block cursor remains to the right of the word
'completion' in the 'Describe function' window.

7. I now move the mouse so that the mouse pointer in over the
completions buffer, and scroll down using the mouse wheel until the
button is visible. I take pic03.png. The non-visible mouse pointer is in
the completions buffer. The non-visible, filled-block cursor remains to
the right of the word 'completion'. A visible, open-block cursor remains
in the scratch buffer, and the second visible open-block cursor remains
in the completion buffer but now encloses the letter C in
'Completion--insert'.

8. I move the mouse to click on the button in the completions buffer,
and take pic04.png. The filled-block cursor that was to the right of the
word 'complete' is now open and visible. There is a non-visible,
filled-block cursor in the completions buffer and is flashing at the
start of the line 'Completion-list-candidate-at-point'. Further tabbing
moves this cursor along the line of completion candidates. The visible,
open-block cursor in the scratch buffer remains.

If relevant, I see exactly the same results if I use openbox or stumpwm
as my window managers, and if I use <RET> rather than <TAB> in Step 5. I
also use a very old monitor and an old version of Debian (9.13).

Let me know if you need anything further.

Best wishes,

Colin.