I said it already: it timeouts or stay still forever without receiving any answer whenever I try to use another interface. For instance, currently I didn’t check the checkbox, so by default it uses tun0, and if I want to use the other interface (currently rj45 cable, that is enp0s25), here what I see:
galex-713@portable:~$ curl –interface tun0 ifconfig.me; echo 89.234.186.82 galex-713@portable:~$ curl –interface enp0s25 ifconfig.me; echo
And I keep a blank line with that command staying still forever until I do Ctrl+C or I disconnect. If I check that checkbox and enp0s25 becomes the default, the opposite happen: I can do that with enp0s25, but tun0 stop being usable.