It seems the Pre release 4.3 still have issues with terrain painting objects:
(EDIT: I had to remove these links as the files are now gone.)
It seems to me that the terrain is still capable of drawing under the terrain (and what are those shadows doing there under the terrain. There should be no light there) as well as not being able to handle anything that get even close to a real forest. As soon as I up the density even a little, trees being to loose textures and turn orange, red, splotches of green while playing etc… at least it didn’t explode in a cataclysm of light this time.
I don’t know if it is possible upload the project files to you so you can have a look, because I don’t think this is right. I don’t know what I am doing wrong, or even if I am doing anything wrong. But if you want the project files, just send me some directions on where to send it (and how to pack it) It is fairly large because of the terrain though (2.8GB)
You are also free to keep the terrain for anything you like (or toss it, give it away etc…) because I created it myself. As for textures, trees etc… you might not want to keep those as they are not very good. And they come from a free source from blender cookie I believe. Don’t remember. I only use them to try things out anyway.
Best regards/
Mike
UPDATE:
I’ve been thinking, it is possible that when I paint, I actually paint inside a “sphere”. Meaning that when I set the paint brush, it sets the radius of the sphere (as opposed to a hemisphere) and it touches the large water polygon under the terrain, thus drawing on it? If this is the case, then it actually is a bug. Because drawing under a terrain should be impossible (I believe) and probably adds to the problem of me not being able to draw a more dense forest. Because I need to be capable of drawing a forest going to the horizon. If the engine solves it by using large imposters at a great distance, so be it. But it looks to me that it isn’t. And that is a problem. That makes it hard to draw to the horizon if the details can’t be faked at a distance. Think clouds, and cloud imposters. This is the motivation as to why I am insisting on drawing on such vast distances 
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