A Ruby Scoping Gotcha?

class TestClass
  attr_accessor :one
  
  def my_method(branch=true)
    if branch
      puts "Do nothing to modify `one`"
    else
      puts "Modify `one` but it's a local variable"
      one = "test"
    end
    
    one # local variable
  end
  
  def my_non_modifying_method(branch=true)
    if branch
      puts "Do nothing to modify `one`"
    else
      puts "Do nothing to modify `one` either"
    end
    
    one #method call
  end
end

o = TestClass.new
o.one = "Value"

puts o.my_method 
 => nil #might expect 'Value' if you're not paying attention
puts o.my_non_modifying_method #expects "Value"
 => "Value"
puts o.my_method(false)
 => "test"
puts o.my_non_modifying_method(false) #expects "Value"
 => "Value"