why ABR flood lsa3 to non-backbone area?

[chan alfie]

hi community,

I got some confused of ospf lsa3.

topology:

     r1 --a12-- r2 --a0-- r3 --a34-- r4
                |          |
                +---a23 ---+

r1(intf:r1r2) and r2(intf:r2r1) are belong to area 12, ptp network: 10.0.12.0/30
r2(intf:r20r30) and r3(intf:r30r20) are composed to area 0, ptp network: 10.0.100.0/30
r2(intf:r2r3) and r3(intf:r3r2) are composed to area 0, ptp network: 10.0.23.0/30
r3(intf:r3r4) and r4(intf:r4r3) are cmposed to area 34, ptp network: 10.0.34.0/30

r1 has a stub net: 10.1.1.0/30
r4 has a stub net: 10.4.2.0/30

why r2/r3 regenerated lsa3 and advertise on area 23, isn't it prohibited ABR to flood lsa3 to non-backbone area?

r2
```
bird> s o l type 3 area 23

Area 0.0.0.23

 Type   LS ID           Router          Sequence   Age  Checksum
 0003  10.0.12.3       10.0.0.2         80000004  1088    6885
 0003  10.0.34.3       10.0.0.2         80000004  1064    d9f3
 0003  10.0.100.3      10.0.0.2         80000004  1088    9cf8
 0003  10.1.1.3        10.0.0.2         80000004  1070    3ab3
 0003  10.4.2.3        10.0.0.2         80000004  1060    6f70
 0003  10.0.12.3       10.0.0.3         80000004  1063    c61c
 0003  10.0.34.3       10.0.0.3         80000004  1069    6f67
 0003  10.0.100.3      10.0.0.3         80000004  1069    96fd
 0003  10.1.1.3        10.0.0.3         80000004  1063    984a
 0003  10.4.2.3        10.0.0.3         80000004  1062    05e3
```
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