If you have more network interfaces, you have more IP addresses.
Actual IP address for a connection is chosen primarily by the target:
If you connect to localhost, you'll probably be connected as 127.0.0.1.
If you connect to some host in your vpn, you'll have IP from your VPN interface.
If you connect to some host in the internet, you'll have IP address of the interface responsible for the internet connection.
The IP address you see on a website is influenced by what is the setting of the VPN: If all trafic is passed through that VPN then you have VPN Interface's address - that's obvious. Check your internet [explorer] setting, if there isn't any proxy set by VPN and check your routing tables when the VPN is connected and disconected. That will answer all your questions.