Bundler confusion during cleanup

Running gem cleanup I'm warned about removing a gem. But they all appear to be ok with a version more current than what they specify. Why am I being warned?

$ gem list bundler
bundler (1.0.13, 1.0.12)

$ gem cleanup
You have requested to uninstall the gem:
    bundler-1.0.12
gherkin-2.3.7 depends on [bundler (>= 1.0.10)]
haml-rails-0.3.4 depends on [bundler (~> 1.0.0)]
jquery-rails-1.0 depends on [bundler (~> 1.0.0)]
orm_adapter-0.0.4 depends on [bundler (>= 1.0.0)]
rails-3.0.7 depends on [bundler (~> 1.0)]
rails3-generators-0.17.4 depends on [bundler (>= 1.0.0)]
thor-0.14.6 depends on [bundler (~> 1.0)]
If you remove this gems, one or more dependencies will not be met.
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Is this due perhaps to dependencies OF dependencies within dependent gems? (scary sentence).

The ~> specifier means "approximately greater than" and 1.0.13 may be just out of range. I'm not sure how loose that specifier is, but usually ~> 1.0.0 will work for any 1.0.x so you should be okay.

You could always archive your GEM_HOME directory and try, then restore if it doesn't work out. You can also re-install a specific version with:

gem install bundler -v 1.0.12