This is a incosistent problem, in which I cannot determine why it's happening and it doesn't happen all the time. I often restart Lightroom and it is ok after that.
In a small area of the screen the curser doesn't function. I cannot select an image or anything in that area while in the library module and when in the develop module brushes change back to the arrow icon and don't allow me to click in that area.
This is my first time using Lightroom and am currently using version 4.3 that I downloaded from the Mac App store. I am running a new MacBook Pro with OS 10.8.2 Mountain lion.