Difference between sharing a Folder to a user or a Group with Subfolders? Permissions weird

I’ve discovered some strange behavior when sharing folders.

I have a folder “A”, in which there are two folders “B” and “C”.

- B
- C

(During testing the folder was synchronized with the nextcloud client (Windows))

When I share the A folder with a user directly (Edit, Create and Delete rights), all subfolders are synchronized. If I now delete a file in a subfolder “B” or “C”, it will be synchronized again after a few seconds, not deleted. (No Errors is shown, and no errors in the logs)

However, if I add the test user (on which was shared before) to a group (with exactly the same permissions), and share the “A” folder to the group instead of the user, I can delete files in the “B” or “C” folder.

Does anyone know the difference between sharing a folder with a user or group?

Thanks a lot in advance,