Docker multi postgres containers with one mount point

I have two Postgres databases and I want to sync data between themes.

So far I have these two containers, exactly the same with different posts and different names.

docker container run --name='p1' -d -p 5435:5432 -v /tmp/dbs/test/:/var/lib/postgresql/data postgres

docker container run --name='p2' -d -p 5436:5432 -v /tmp/dbs/test/:/var/lib/postgresql/data postgres  

The problem happens when something changed.

If I change something in p1 like insert a row, then I can’t see it in p2.

But if I kill, and run containers again, then I can see the inserted data in both of themes.

Why this is happening?
Is there a way to sync data between themes?

Source: Docker Questions