Latitude 6520 Touch Pad issue help needed

I have one glitch that bothers me right now. When using the touch pad sometimes when I move the curser to type in a open or partially used box then tap to start the curser blinking so I can type it doesn't work. I have to use any of the enter buttons to start. Not all the time just sometimes. I can't seem to figure out what's triggering it. Never had that problem with my C640 touch pad.