multicast works even if interface is out of route table

Hello everybody.

I'm a bit confused about this:

I'm testing a minilab:

*R1* - 10.0.12.0/24 - *R2* - 10.0.23.0/24 - *R3*

R1 is the receiver (ip igmp join 224.1.1.1 on loo 0)
R2 is the server (ping 224.1.1.1 rep 100)
R3 is the autorp
ospf is the igp

ok, everything works.
if I shutdown the R1 L0 interface the ping stop to reply. OK, fine.
but if the R1 L0 is up but not configured to be part of OSPF process the
ping to 224.1.1.1 is still working and replies come from 10.0.12.1

(already cleared ospf and ip mroute *)

I don't get how this is possible.. someone can explain this?

thanks

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