New Layer Difference Mode broken

I open a (raw image). I (on a Mac) use Cmd-shift-N to create a new layer. In the dialog box I chose Difference as the blending mode. I then attempt to fill the layer with white, which should give be a negative image. Nothing happens. However, if I make that layer invisible, then the layer below it shows up in negative. THis also happens if I create the new layer from the context menu and select Difference at that time.This does NOT happen if I make the new layer with Ctl-Shift-N and then set the blending mode in the Layers panel. It only began with the latest update (21.2.0 on Mojave)