Explanation/Reference:
Tunneling IPv6 Traffic over MPLS IPv4 Networks
D: You enable IPv6 tunneling by including the ipv6-tunneling statement in the configuration for the PE routers.
A: BGP automatically runs its import policy even when copying routes from a primary routing table group to a secondary routing table group. If IPv4 labeled routes arrive from a BGP session (for example, when you have configured the labeled-unicast statement at the [edit protocols bgp family inet] hierarchy level on the PE router), the BGP neighbor's import policy also accepts IPv6 routes, since the neighbor's import policy is run while doing the copy operation to the inet6.3 routing table.
References: http://www.juniper.net/documentation/en_US/junos15.1/topics/example/mpls-tunneling-ipv6- over-mpls-ipv4.html