help-block doesn't hide or display

[Dreyfuzz]

Here's my markup validating an iTunes store url:

    <form id="new_app">
        <div class="control-group">
            <div class="controls">
                <input type="text" name="name" id="new_app_name" placeholder="Enter app name">
                <input type="text"
                  pattern="^(https?:\/\/)?itunes.apple.com\/us\/app\S*$"
                  data-validation-pattern-message="Must be a valid app store link"
                  name="app store link" id="new_app_url"
                  placeholder="Paste App store link">
                <input type="submit" value="Submit for Review">
                <p class="help-block"></p>
            </div>
        </div>
    </form>