Nginx uses latest vhost as default server?

For some reason, it seems like the virtualmin implementation of nginx is using the most recently created vhost as the default.

So if I visit the IP address of the server, or a domain which is pointing to the IP but not configured in nginx (e.g. the server's hostname), I get the content of the most recent vhost that I created.

I cant work out why, when I tried out nginx without virtualmin before, then it would use "default" as the default config for any domains/IPs without their own "vhost" config.

Any ideas?