Configuring the management LAN on an M4100-26G-POE

For home use, I bought a used M4100-26G-POE as a replacement for my JGS-516PE. Primary reason for this, is the fact that the JGS516 exposes the management interface untagged on all ports, which I do not like. 

At first I started with a factory default and updated the firmware of the M4100 to the latest version: 10.0.2.35, B1.0.1.1 

Now I am spending already 2 evenings attempting to configure the management LAN, but without success. It seems somehow, something simple is overcomplicated or just does not work. 

First question: In the management interface config screen is an option "Routing Mode" with enable/disable.
I could not find an explanation what it actually does. As a sidenote:  I am not planning (yet) to use any L4 functionalities. Only L2 switching.

Currently, I can access the GUI on the default 169.254.100.100 (untagged)

In the "switching->VLAN config"  menu I defined a VLAN :   ID=10  type=static
VLAN 10 is tagged on Port 1 and untagged with PVID set to 10 on port 25. 

In the VLAN status overview,  there is "routing interface" 4/1 for VLAN 1 and 4/2 for VLAN 10. What does this mean and where does this come from ?

In the management config page I selected VLAN ID 10, entered IP 192.168.10.20  and subnet mask. No DHCP. 

After pressing apply and after reboot, the VLAN is still accessible on the original 169.254.100.100 IP address. 
When selecting VLAN 1 on the management config page, I see the default address and when I select VLAN 10 on the config page, I see the 192.168.10.20 address.  Tried to open the webpage on the untagged port with 192.168.10.20, but without success. 

The displayed "Management VLAN ID" on the config page stays on '1' even after selecting '10' and apply. 

What am I overlooking, it can't be that complicated. Any help would be appreciated.