git pull merges by default, when it should really rebase. You can ask it to rebase instead, but it still won't touch anything other than the currently checked-out branch. If you're tracking a bunch of remote branches, you'll get non-fast-forward complaints next time you push.
Solve it once and for all:
git-up might mess up your branches, or set your chest hair on fire, or be racist to your cat, I don't know. It works for me.
git-up can check your app for any new bundled gems and suggest a
bundle install if necessary.
It slows the process down slightly, and is therefore enabled by setting
true in your git config, either globally or per-project. To set it globally, run this command anywhere:
git config --global git-up.bundler.check true
To set it within a project, run this command inside that project's directory:
git config git-up.bundler.check true
Replace 'true' with 'false' to disable checking.