Samsung Galaxy S4 WiFi problem after update

[Downunder35m]

For many users the update to 4.3 or 4.4 not only Knox but also for some problems using the WiFi.
There are those that flashed manually and might have used the wrong modem file, but that is not my concern here.
I updated the official way using Kies and shortly after I was unable to get into the internet using WiFi.
Tried the obvious fixed by removing my network and set it up again, changing the Wifi setting in my router but nothing helped.
The "fixes" offered on the net went from a hard reset to a flash using Odin, which would set the Knox flag and void the warranty apart from disabling all Knox features.
But most of the affected user on the net also got an error message in the notification bar, which I did not get.
Further checks showed that my phone is connecting to my router by has the assigned IP address of "::1" - which can't work at all.

To fix do a long press on the connection to your router within the WiFi screen.
From there on "modify network config".
Tick the box "Show advanced options".
Scroll down to IP settings and change from "DHCP" to "Static".
Assign an IP address within the range of router - for example 192.168.10.3 if your router has the address 192.168.10.1

After that my Wifi worked as flawless as before.
It seems to be a bug that messed with the WiFi config file after the update.
Going back to "DHCP" works for a while but stops working once you try to connect while another device uses the IP you entered manually in the above step.
Before the next official update I will do a full backup and factory reset