GRE tunnel still up/up despite keepalive

The network topology looks like this: Router 1 tunnel — ISP — Router 2 tunnel

The tunnel configuration for both ends of the tunnel are as follows:

ip address x.x.x.x no ip redirects no ip unreachables no ip proxy-arp ip ospf hello-interval 3 ip ospf cost x keepalive 10 3 tunnel source x.x.x.x tunnel destination x.x.x.x 

Even when router 2 is down and inaccessible, the tunnel at router 1 is still showing up/up despite keepalive being configured.

Routers are Cisco devices.

Any ideas why is this so?