OES2015SP1 Server (fully patched) gets updated by booting the OES2018SP1 DVD. DUring the upgrade, german keyboard gets specified (language is english), and works. During the first boot stage, the keyboard is still german (I know this because the admin password contains characters that I'd notice). Once the upgrade is complete, I patch the server from a local SMT.
After that, the console keyboard is suddenly english, but is still set to german in "yast keyboard". To get it back to german again, I have to change it to something else and back to german.
100% reproducible so far on every upgrade.