Richie,
Layer objects tend to work best in a manual depth sorting mode. This is what I would suggest. Take the remaining objects and put them in their own layer object. I will often make a layer object called "mask" and another called "main" that contains everything I do not want affected by the mask.
Now take the two layer objects and move them above and below one another in the object manager and you will see the render priority change. This should fix the problem.
Andrew
#Carbonite