: matters?

When I run cucumber, cucumber told me there is a Ambiguous match:

Feature: Login
  In order to login
  As an API client
  I want to login as a valid user

  Scenario: I login as an valid user                                 # features/login.feature:7
    Given User "user" exists with password "password" and id "1"     # features/step_definitions/login.rb:1
    When I send a POST request to "/api/v1/login" with the following # features/step_definitions/login.rb:5
      """
      {
        "name":"user",
        "password":"password"
      }
      """
    Then the response status should be "200"                         # features/step_definitions/login.rb:9
    And the JSON response should be:                                 # features/login.feature:17
      """
      {
        "user_id": 1
      }
      """
      Ambiguous match of "the JSON response should be:":

      json_spec-1.1.4/lib/json_spec/cucumber.rb:13:in `/^the (?:JSON|json)(?: response)?(?: at "(.*)")? should( not)? be:$/'
      features/step_definitions/login.rb:13:in `/^the JSON response should be:$/'

      You can run again with --guess to make Cucumber be more smart about it
       (Cucumber::Ambiguous)
      features/login.feature:17:in `And the JSON response should be:'

Failing Scenarios:
cucumber features/login.feature:7 # Scenario: I login as an valid user

1 scenario (1 failed)
4 steps (1 failed, 3 passed)
0m0.158s

I removed colons(:) in the scenario and the corrsponding step_definision, then it passed. Although I can use cucumber --guess to make this scenario pass but I just don't like it. I'm not sure if the colon really matters but seemed it affects cucumber a bit.

Feature: Login
  In order to login
  As an API client
  I want to login as a valid user

  Scenario: I login as an valid user                                 # features/login.feature:7
    Given User "user" exists with password "password" and id "1"     # features/step_definitions/login.rb:1
    When I send a POST request to "/api/v1/login" with the following # features/step_definitions/login.rb:5
      """
      {
        "name":"user",
        "password":"password"
      }
      """
    Then the response status should be "200"                         # features/step_definitions/login.rb:9
    And the JSON response should be                                  # features/step_definitions/login.rb:13
      """
      {
        "user_id": 1
      }
      """

1 scenario (1 passed)
4 steps (4 passed)
0m0.158s