OSPF NSSA P-bit Explained

hi,

Although advertising router is 192.168.234.3, how can R1 learn 4.4.4.4 from both of the R2 and R3? Why does not it learn only from R3?

R1#show ip route ospf | begin 4.4.4.4
O E2     4.4.4.4 [110/20] via 192.168.13.3, 00:38:49, FastEthernet0/1
                 [110/20] via 192.168.12.2, 00:38:49, FastEthernet0/0

R1#show ip ospf database external

            OSPF Router with ID (192.168.13.1) (Process ID 1)

                Type-5 AS External Link States

  Routing Bit Set on this LSA in topology Base with MTID 0
  LS age: 1346
  Options: (No TOS-capability, DC)
  LS Type: AS External Link
  Link State ID: 4.4.4.4 (External Network Number )
  Advertising Router: 192.168.234.3
  LS Seq Number: 80000001
  Checksum: 0xFAE5
  Length: 36
  Network Mask: /32
        Metric Type: 2 (Larger than any link state path)
        MTID: 0
        Metric: 20
        Forward Address: 192.168.234.4
        External Route Tag: 0

regards,