I think I've accidentally found a bug during installationprocedure.
During setup, when you define a static IP, if you make a mistake (I added on '.' too much in netmask), you get a warning that the entered netmask isn't correct.
You get back to the option where you can select to set up Static IP again.
After typing all the correct info, it starts installing, but at the same time you see "wrong calculation for netmask".
After rebooting the system, and starting the install again, everything works normal again.