[shoulda-matchers gem] validate_numericality_of_matcher strange behaviour

[alex]

Hello
I have Vacancy model and vacancy_spec test with validates_numericality_of :salary, greater_than: 1 in the model and
validate_numericality_of(:salary).is_greater_than(2) in the _spec.
When i run rspec spec command tests pass (in some cases and in other they don't)
Why?

vacancy.rb
------------------------
class Vacancy < ActiveRecord::Base

  validates_presence_of :name, :salary, :position, :description, :company,
                        :contact, :location
  validates_length_of :name, :position, :company, :contact, :location, in: 3..50
  validates_length_of :description, in: 3..250
  validates_numericality_of :salary, greater_than: 1
end

vacancy_spec.rb
--------------------------
require 'spec_helper'

describe Vacancy do

  [:name, :salary, :position, :description, :company, :contact, :location].each do
    |value| it { should validate_presence_of(value) }
  end

  [:name, :position, :company, :contact, :location].each do
    |value| it { should ensure_length_of(value).is_at_least(3).is_at_most(50) }
  end
  it { should ensure_length_of(:description).is_at_least(3).is_at_most(250) }
  it { should validate_numericality_of(:salary).is_greater_than(2) }

end
----------------------------------

Console output: (I'm running the same spec)
~/ror/test_app2$ rspec spec/models/vacancy_spec.rb
..............

Finished in 1.46 seconds
14 examples, 0 failures

Randomized with seed 36106

~/ror/test_app2$ rspec spec/models/vacancy_spec.rb
..............

Finished in 1.48 seconds
14 examples, 0 failures

Randomized with seed 898

~/ror/test_app2$ rspec spec/models/vacancy_spec.rb
.....F........

Failures:

  1) Vacancy should only allow numeric, integer values for salary
     Failure/Error: it { should validate_numericality_of(:salary).is_greater_than(2) }
       Expected errors  when salary is set to 2, got errors: ["name can't be blank (nil)", "name is too short (minimum is 3 characters) (nil)", "position can't be blank (nil)", "position is too short (minimum is 3 characters) (nil)", "description can't be blank (nil)", "description is too short (minimum is 3 characters) (nil)", "company can't be blank (nil)", "company is too short (minimum is 3 characters) (nil)", "contact can't be blank (nil)", "contact is too short (minimum is 3 characters) (nil)", "location can't be blank (nil)", "location is too short (minimum is 3 characters) (nil)"]
     # ./spec/models/vacancy_spec.rb:20:in `block (2 levels) in <top (required)>'

Finished in 1.49 seconds
14 examples, 1 failure

Failed examples:

rspec ./spec/models/vacancy_spec.rb:20 # Vacancy should only allow numeric, integer values for salary

Randomized with seed 60725