Microdisplacement alpha problem/bug (Arnold for Houdini)

[otto33]

Hi, I'm having the following problem when rendering a scene with microdisplacement in HtoA,

This is what my scene looks like, a simple plane with an adaptive subdivision setup:

 

And this is how it looks rendered (as you can see, even though the plane didn't originally cover the entire camera view, it does once the subdivision comes in for the render, which is expected):

 

Now here is the problem, as soon as I add any other mesh into the scene (it doesn't matter what kind), this happens:

The actual structure of the landscape remains the same, but the alpha gets clip to the alpha that the original un-subdivided plane would have had.

 

Any idea how to solve it?

Thanks in advance,