Summation of effort estimates in columnview dblock

[Alexander Adolf via "General discussions about Org-mode." <emacs-orgmode@gnu.org>]

Dear Org Developers,

I'm using Org 9.7.9, and I'm seeing behaviour of the (undocumented?)
"%Effort" vs. "%Effort{:}" in the column view dblock, which confuses me.

Consider this example:
---------------------------- Begin Quote -----------------------------
#+BEGIN: columnview :maxlevel 1 :indent t :format "%ITEM(Task) %EFFORT(Estimated) %EFFORT(Estimated Total){:}" :id global
| Task   | Estimated | Estimated Total |
|--------+-----------+-----------------|
| Task 1 |        2d | 7d 0:00         |
#+END:

#+BEGIN: columnview :maxlevel 2 :indent t :format "%ITEM(Task) %EFFORT(Estimated) %EFFORT(Estimated Total){:}" :id global
| Task         | Estimated | Estimated Total |
|--------------+-----------+-----------------|
| Task 1       |        2d |         7d 0:00 |
| \_  Task 1.1 |        3d |              3d |
| \_  Task 1.2 |        4d |              4d |
#+END:

* Task 1
:PROPERTIES:
:EFFORT:   2d
:END:

** Task 1.1
:PROPERTIES:
:EFFORT:   3d
:END:

** Task 1.2
:PROPERTIES:
:EFFORT:   4d
:END:
----------------------------- End Quote ------------------------------

I would have expected the estimated total (rightmost column) for "Task
1" (first body row) in both dblocks to be 9 days (instead of seven)?

What am I missing?


Many thanks in advance and cheers,

  --alexander