Problems with grasping an object: need to wait 15s until the object gets attached to the gripper

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As explained in this ROS answer, I have had a lot of problems until managing to grasp a 2.5 cm cube on gazebo with a turtlebot arm. The remaining problem is: why I need to wait so long until the cube gets attached to the gripper? If I don't wait the 15s, the arm elevates without the cube, as in this video. Same applies to detaching: I need to wait around 5 seconds with the gripper open before leaving the placed block. Other people using ROS-Moveit!-Gazebo seem to have the same problem, but nobody on ROS answers came with an answer. Any clue?

I suppose that the parameters attachsteps and detachsteps I must add to the robot URDF file have something to do with this, but I cannot find any documentation, nor get any benefit when modifying them:

  <gazebo>
    <gripper name="gripper">
      <grasp_check>
        <attach_steps>5</attach_steps>
        <detach_steps>10</detach_steps>
        <min_contact_count>2</min_contact_count>
      </grasp_check>
      <gripper_link>gripper_active_finger_link</gripper_link>
      <palm_link>gripper_static_finger_link</palm_link>
    </gripper>
  </gazebo>

I use Gazebo 2.2.3 with ROS indigo.

Thank you a lot!