R&S v4.0 WB-1 9.24 IPv6 MP-BGP

Wondering why the network statement is not "Network 2003:1:0:11::/61? 



R1:
interface Loopback 101
 ipv6 address 2003:1:0:1::1/64
!
interface Loopback 102
 ipv6 address 2003:1:0:11::11/61
!
router bgp 100
 address-family ipv6 unicast
  neighbor 2001:1:0:1234::5 remote-as 500
  neighbor 2001:1:0:1234::5 activate
  network 2003:1:0:1::/64  network 2003:1:0:10::/61
  aggregate-address 2003:1::/59 summary-only