Why do a series of specs fail when each single spec succeeds?

Question

On Capybara 2.1.0 with Rspec 2.12.0:

If I run $ rspec spec/features/user_sees_leaderboard_spec.rb, the spec passes.

If I run $ rspec spec/features/*, the test fails, claiming:

Capybara::ElementNotFound:
   Unable to find css "#flash"

If I do save_and_open_page, #flash is present and visible.

Here's the helper where the failure is occurring:

def sign_in_as(user)
  visit new_user_session_path
  fill_in "Email", with: user.email
  fill_in "Password", with: user.password
  click_button "Sign In"
  flash = find("#flash")

  flash.should have_content "You are now signed in."
end

Any ideas? I'm new-ish to Capybara so not sure where to start. Thanks!

EDIT/UPDATE:

By doing save_and_open_page on a set of specs that fail when run together I was able to see a series of successes followed by a series of pages saying nothing besides "Not Found" in the body tag. Google didn't turn up anything – thoughts?

UPDATE #2

I noticed that the "Not Found" content in BODY began just after a spec that used capybara-webkit to run javascript. Even explicitly resetting Capybara.current_driver = :rack_test in an after(:all) block doesn't fix the issue, but I think this is relevant.

Answer 1

While still not 100% sure what caused this, removing Capybara.automatic_reload = false from the tests using capybara-webkit resolved the issue.