Hi bmarkus.
Just tested an idea.
Doing all this via ssh using dropbear results in my previous findings, that changes does not survive a reboot.
However, working directly at the rpi with a keyboard, then the changes do survive a reboot.
So somehow there is a problem using ssh and dropbear.
I don't know if it has any importance but in order to use dropbear, I had to make a password for user tc. But it is not different from what I did in version 4.7.7 and here everything is well also via ssh and dropbear.
Steen