Release pipeline is triggered with master yml after merging to master

- The development for project X is done in master.

- There is a pipeline for project X for master to run some tests after merging a PR to master. The corresponding yml is called X.yml

- Recently we branched out the master to a new branch called release_branch.

- release_branch contains everything master has, but is frozen, master moves on. X.yml exists also in release_branch and contains less stages than the X.yml that exists on master.

- X.yml in release_branch differs from X.yml also in triggers settings: X.yml in release branch is setup like:

trigger:
  batch: true
  branches:
    include:
      - release_branch
  paths:
    include:
      - projects/X

and on master:

trigger:
  batch: true
  branches:
    include:
      - master
  paths:
    include:
      - projects/X

- After merging a PR on release_branch, only release_branch pipeline is triggered and runs the tests that exist on X.yml existing inside the release_branch, which is ok and expected.

- The issue is that after merging a PR on master, both master and release_branch pipelines will be triggered and both will run under the X.yml that exists on master. We cannot understand why release_branch pipeline is trigger after merging a PR on master, and runs under the master X.yml. After merging a PR on master, we would like only master pipeline to be triggered. What seems to be wrong in our setup?