I am having some minor problems with my garage door opener. When the door is closed and push the inside door button once, and the door will raise with no problems. Now to close the door, you push it once, and the door will start to close, but then the door will go right back up. But if you hold that button down, then the door will close. I am not understanding why the door will close. The sensors are not blocked. There is nothing in the way to prevent the door from closing. Please help.