git checkout tag, git pull fails in branch

Question

I have cloned a git repository and then checked out a tag:

# git checkout 2.4.33 -b my_branch

This is OK, but when I try to run git pull<

Answer 1

@alesko : it is not possible to only do only git pull after checkout my_branch to update master branch only.
Because git pull will also merge to the current branch -> in your scenario to the my_branch

@Simon: that will do also the push. why is that?

$ git branch -u origin/master
Branch master set up to track remote branch master from origin.

and acording to docs:

-u 
  Set up 's tracking information so  is considered  
  's upstream branch. If no  is specified,  
  then it defaults to the current branch.