I am observing the following behavior:

1.- Fresh installation, installing latest version of Pipeline, GitHub plugin and GitHub Branch Source Plugin

2.- Manage Jenkins > Configuring GitHub plugin: Credentials of an Owner of a Organization which hosts a Repo X

3.- New Pipeline Multibranch Item pointing to Repo X, after saving the job the webhook in GitHub is not automatically generated (vs. GitHub Organization Folder item which is done)

4.- Manage Jenkins > GitHub plugin > Advanced > Re-register hooks for all jobs > webhook in GitHub is finally generated
 
What I am reporting: I'd expect the webhook in GitHub is automatically generated right after the saving the Pipeline Multibranch Branch but it does not it until I click on Re-register hooks for all jobs (GitHub plugin)