No bug here. As seen by Statistics, a CFA or RGB Bayer image is just a regular image. The Statistics tool promises that the numbers you get are properties of the actual pixel data in the image, without any manipulation. So if the image has 'black holes' (as a RGB Bayer frame) then that's what you get. The same happens with the rest of image analysis tools; HistogramTransformation for example.
An important design rule in PixInsight is that the platform does not depend on hardware-specific features at the high levels. For example, the [0,1] range is the native range in PixInsight for the same reason. It is an abstract range that is independent on any particular bit depth and numeric format. This enforcement of abstract representations is one of the strongest points of the PixInsight platform.
