Automaticly deselect Clip after seperating

That would be illogical behaviour. There's nothing you can do with two selected clips that you've just split without deselecting one of them anyway, and no you can't alter this behaviour. More to the point, this would also have been illogical in Audition 3, so I just tried splitting a clip in it to see if it does indeed do what you say. And it doesn't. You put a split in a selected clip, and both sides of it are deselected. So I don't know what you've done, or whether you've described it incorrectly, but it certainly doesn't do what you've described here, I'm afraid.