I've had this issue for the latest 2 builds, when i render using DR, the frame buffer Beauty pass will go black randomly after a few minutes, then if I cycle between the elements and back to beauty it will show up again, then go black after some minutes. When render ends it is randomly either saving or not saving the beauty (black layer) depending on if it shows or not at the time. In some cases the other elements also would have the alpha wrong as in a big blag square of the element missing or added. Anyone having same issue? could it be a memory leak when it receives data from the render nodes?