Elasticsearch CCR, former follower (leader) index is not writable

[Armen_Petrosyan]

I use ES 7.7.1

Below UC that I am trying to test:

1. I have two clusters leader and follower. On leader I have created index, and alias.
2. Starting follow process, I see that index replicated to the follower as well as alias. Everything is good.
3. I am starting unfollowing process (pause, close, unfollow, open)

Expected
Two different 'leader' clusters. I have an ability to write to former follower (leader) as well as to original leader.

Actual
I try to index some document to former follower (leader), I am getting error saying that index is not writable.

Investigation
I starting to check indices and see that in original cluster

{
"aliases": {}
}

However in follower cluster I see

  }
  "aliases": {
    "MyIndex": {
      "is_write_index": false
    }
  }

Question

1. How come that after replication value of "is_write_index" changed to false. Is it expected behavior?
2. If it is expected behavior, should I update "is_write_index" to be true on former follower (leader) in order to continue index documents to it?

P/S - I am reading what is is_write_index in documentation, and see that here description of this flag contradicts with description on this page

[Armen_Petrosyan]

Anyone?