When I push a commit with a tag, why does default step also run?

[Grant Pierce]

I have a bitbucket-pipelines.yml set up this way:

image: node:11-alpine
definitions:
  steps:
   - step: &build-and-test
     name: Get dependencies and test
     caches:
       - node
     script:
       - yarn
       - yarn test
  steps:
   - step: &bump-version
     trigger: manual
     name: Updating version
     script:
       - apk add git
       - yarn bumpversion
pipelines:
  tags: 
    'v*.*.*':
    - step: 
      name: Deploy to Test
      deployment: Test
      script:
        - SOME DEPLOYMENT STEPS    
  default: 
    - step: *build-and-test
    - step: *bump-version  

The idea is that every commit runs *build-and-test. Then *bump-version is a manual step if we want to deploy it. Bump-version pushes a new version tag. and I would expect the v*.*.* pipeline to run off that new commit, which it does. But default pipeline also runs again. Is there a way to run the tag pipeline exclusively? 

FYI yarn bumpversion is a package.json scrpt that runs 

yarn version --patch && git push --follow-tags

After that push, both steps are triggered, even with the same commit hash.

[Grant Pierce]

Editted question