Repro 1: Create a new image Fill the image with half-transparent white Run Gaussian Blur at default radius; the whole image should noticeably darken The image is noticeably darker. Check the color channels; they're definitely not white anymore Before|After Repro 2: Create a new image Delete a section in the middle of the image Run Gaussian Blur at default radius Repeat with Ctrl+F until you see edges darkening; should be noticeable on the 5th time, and painful on