Hello Alvaro
Yes Alvaro, that makes sense. Poison reverse will cause R1 not to put the routes in the routing table. However, once you reinstate the summary route, after a certain amount of time, the poison reverse message will have timed out, this is how it should function. During the time that the networks are still “poisoned” can you use show ip protocols and show ip rip database and you can also continue to watch RIP debugs to see if/when the poison updates stop and if/when the networks get reinstated. Once the poison reverse updates expire, the networks should get reinstated. If not, with the tools mentioned, you should be able to determine why not.
Poison reverse is useful in networks where you may have routing loops. If you had a third router in your topology, then R1 may have removed the summary routes and sent out a route poison update to R2, but in the meantime, R3 may send one of its periodic updates indicating that it has a route to the (no longer available) summary route, and R1 may reinstate it even though it was removed. More information on reverse poisoning can be found in this lesson which explains it in detail.
I hope this has been helpful!
Laz