Wrong keyboard layout at first logon after RUM move

Hey guys,

we are just in the middle of an AD migration project and from technical point of view most things are working fine and we have only slight issues.
But we have seen one issue what might cause a lot of confusion. Directly after the client migration, some users have issues to logon,
because the keyboard format has been swapped from German to English US or vice versa. During the first logon it is not visible which
language format is chosen and so this results in a lot of typos for entering the password.
After the logon everything is fine again and if you check the region formats it has not been changed.

Do you guys have an idea, how this can happen?
Thanks in advance.