Sorry. I messed up the previous mail. Please ignore it.

I wrote:

> org-babel-tangle on
>
>   * A
>
>     #+BEGIN_SRC elisp :tangle yes :noweb yes
>     ;; A
>     <<B>>
>     #+END_SRC
>
>   * COMMENT B
>
>     #+BEGIN_SRC elisp :noweb-ref B
>     ;; B
>     #+END_SRC
>
>   * COMMENT C
>
>     #+BEGIN_SRC elisp :tangle yes
>     ;; C
>     #+END_SRC
>
> produces a file with A and B in it. Expected: Just A. Changing
>
>     #+BEGIN_SRC elisp :noweb-ref B
>     ;; B
>     #+END_SRC
>
> to
>
>     # #+BEGIN_SRC elisp :noweb-ref B
>     # ;; B
>     # #+END_SRC
>
> does yield the expected result.

Attached is a patch that fixes the problem.

A second patch is attached that contains tests about this and related
stuff. It is an updated version of an unapplied patch that I
sent to this list earlier this month
(https://lists.gnu.org/archive/html/emacs-orgmode/2019-10/msg00013.html).

Best wishes
Sebastian