mirror paint texturing cycles

Trying to mirror paint texturing in cycles gives me speckled paint how to solve this ?

I have applied the mirror modifier for making good UV unwrap images. Then added a new mirror for use with texture paint.
Painting is getting speckled ! I use cycles and blender 2.68.

Texture Painting with mirror modifier is working fine if the mirror modifier for the mesh is not applied in object mode.
But then I have no good UV image.

I Know it is not a big issue because I can edit uv image externally with gimp.

Another problem is how to hide vertices with ctrl+L for better Texture painting.