[HELP] LandscapeLayerBlend height blend problem

Hey all. I am trying to use the LandscapeLayerBlend node in conjunction with height blending/masking on my terrain. It seems to be working partially but I am seeing the second texture bleed past the mask. Please see the image. From what I understand I should be able to get a clean mask.

Can somebody help me troubleshoot?

Thx

https://dl.dropboxusercontent.com/u/2071787/Swamp/help_heightblend.jpg