I'm not sure if this really is a bug. If you play enough with displacement intersection, in close-up!, then you'll see that at many settings some of the underlying terrain will "shine through".
You can consider these patches as a bug, but it might well be a settings thing.
For instance, the lower the intersection zone, the less obvious these effects tend to be.
But yes....until Matt hasn't made the effort to explain us how this really works and how to use it properly we'll have no real idea whether to consider it as a bug or not.
So Matt...if you don't mind
Cheers,
Martin