I am on XP and see that same problem Only when I turn on the G-buffers & render without the alpha channel checked.  
If I have just the alpha or the alpha plus the G-buffers on it renders the channels correctly.
Pre-multiplied on or off does not effect the G-buffers showing up in the color channels.
The 2 G-buffers that cause the bleed over into the color channels when the alpha is left off are 3D Position & Normal Vector.
Again this is on the windows build, it "works" the same way in C5 pro.

wayne k
guam usa