Filters are affecting each other in the order they are specified! If the original image has the size 60x40 and the thumbor url would look like:


then the image will first checked if it fits into 100x100 (which it does), then gets the watermark, then it will be blurred (including the watermark), then filled with red so that it will use the 100x100 size and at the end upscaled will be applied without having any effect because fill was changing the size of the image already to the maximum available space.