The filter works correctly, but the preview is misleading when the target is a non-destructively transformed (non-destructively scaled, rotated, etc) Pixel object. In the preview, the filter is being applied to a display representation of the Pixel object, and that representation has been created by resampling the transformed unfiltered pixels of the Pixel object to the document pixel grid.  When the filter is applied, it is applied to the pixels of the actual Pixel object, and then a