Capybara doesn't care about event.preventDefault

Testing Ruby on Rails application with RSpec, Capybara and Selenium.

I want to click an anchor which has an href but shouldn't lead anywhere due to the event.preventDefault. Nonetheless the link leads the test to the linked page instead of remaining on the current one.

My first impression is that Javascript isn't working. Besides for other tests I can see Firefox doing some stuff, but I can say the same thing for this specific test. Is there anything I'm missing?

If I test the page on the dummy app event.preventDefault works as intended.

Current test is:

describe "In field group editor, user", type: :feature do

    let(:user) { User.first }

    before(:context) do
        @structure = create(:structure)
    end

    it "should be able to create a checkbox" do
        sign_in user

        # should be login page
        save_and_open_page # and it is

        path_to_structure = edit_structure_path( structure_id: @structure.slug )
        visit path_to_structure

        find "#add-new-setting"

        # should be structure page
        save_and_open_page # and it is

        click_on "add-new-setting" # this should fire an ajax call and preventDefault link behaviour

        # should be still structure page
        save_and_open_page # instead capybara it's gone to the new setting page

        # ...
    end
end