Gateway Switching under ->System ->Routing not working

[mio-pfsense]

Hi all,
I have set up a new pfsense v2.6 with a totally simple setup:
WAN and LAN interface with static IP.
The WAN Interface has its default gateway set and can access the internet.

I have added a second gateway under ->System ->Routing and want to switch manually between these two gateways.
However if I switch to the other gateway under ->System ->Routing and then the drop down filed under "Default gateway IPv4", the firewall keeps communicating via the existing gateway.
Choosing the other gateway in this drop down field doesn't change anything, also after a state reset.

I have no policy based routing in the LAN interface firewall rules, it's just the default to any rule with the default gateway.

Is there something broken or do I have to use this scenario in a different way?

P.S. If I change the gateway in the WAN interface, it works and I can switch between both gateway. But isn't this supposed to be done via ->System ->Routing ->Drop down field?

Thanks guys!