[Bug Report] Git does not push signingkey ID to GPG

[Oliver Niebuhr <oliver.niebuhr@oliverniebuhr.de>]

Hello.

Using 'git commit -S' (uppercase S) to gpg sign a commit does not work. 
It seems that Git does not push the ID to GPG.

When I use 'git commit --gpg-sign=[KEY]', it works as expected.

What do I try to achieve: Automate adding 'Signed-off-by' and 
automatically sign with the gpg key.

It should work from CMD Line as well from within an IDE.

I have edit the .gitconfig File accordingly and added

[user]
signingkey = NNN
[commit]
gpgsign = true
[alias]
amend = commit -S -s --amend
cm = commit -S -s
commit = commit -S -s
tag = tag -S -s
[gpg]
program = C:\\Program Files (x86)\\GnuPG\\bin\\gpg.exe

The Git User Name and eMail Address are the same which are set in the 
used GPG Certificate.

Using '-S' from the Windows CMD Shell and Git Bash leads to an error. 
Neither typing the command manually or using it through an alias works.

When I switch '-S' with '--gpg-sign=NNN' everything works as it should 
from CMD Line - but not when I use for example SmartGit and enable 'Sign 
all Commits'. After countless hours looking through the Web, I am not 
out of Ideas.

Here is the Trace:
C:\Dev\GitRepos\Test>git cm
00:30:36.873133 exec-cmd.c:237      trace: resolved executable dir: 
C:/Dev/Git/mingw64/bin
00:30:36.874133 git.c:744           trace: exec: git-cm
00:30:36.874133 run-command.c:667   trace: run_command: git-cm
00:30:36.876134 git.c:396           trace: alias expansion: cm => commit 
-S -s
00:30:36.876134 git.c:805           trace: exec: git commit -S -s
00:30:36.876134 run-command.c:667   trace: run_command: git commit -S -s
00:30:36.883142 exec-cmd.c:237      trace: resolved executable dir: 
C:/Dev/Git/mingw64/libexec/git-core
00:30:36.884143 git.c:455           trace: built-in: git commit -S -s

hint: Waiting for your editor to close the file... 00:30:36.889147 
run-command.c:667       trace: run_command: GIT_INDEX_FILE=.git/index 
'"C:/Dev/GitGuis/GitExtensions/GitExtensions.exe" fileeditor' 
C:/Dev/GitRepos/Test/.git/COMMIT_EDITMSG
00:30:45.064284 run-command.c:667       trace: run_command: 'C:\Program 
Files (x86)\GnuPG\bin\gpg.exe' -bsau ''
gpg: skipped "": Invalid user ID
gpg: signing failed: Invalid user ID
error: gpg failed to sign the data
fatal: failed to write commit object

Windows: Windows 10 Pro, 21H1, 19043.1100
Git Version: git version 2.32.0.windows.2
GPG Version: gpg (GnuPG) 2.2.28, libgcrypt 1.8.8, Copyright (C) 2021 g10 
Code GmbH

Thank you in advance!
Oliver Niebuhr