Color picker reports old value on same location across layers with alpha enabled

Environment/Versions

  • GIMP version number: 3.0.6 and 3.2.0-RC2
  • Package: Flatpak
  • Operating System: Arch Linux
  • (if Linux) Display system: X11

Description of the bug

Recently I was comparing image differences across layers, but when using the color picker on layer A and layer B on the same pixel which were definitely different the color picker reported the same value. I had to instead pick the pixel on layer 1, another pixel on layer 2, then the same pixel as layer 1 again. The difference in this case is very small, imperceptible.

Edit: The real world workflow/use case I have is dumping screenshots from a graphics application as well as imagemagick compare layers on top of each other and inspecting the color values using GIMP. In this case even though imagemagick compare shows a different pixel GIMP wouldn't report a different color.

Reproduction

Is the bug reproducible? Always

Reproduction steps:

  1. Open GIMP
  2. Create a new image of any size
  3. Fill the background layer with ffffff
  4. Create a new layer
  5. Fill the new layer with fffffe
  6. Open the color picker and enable the info window
  7. Pick pixel at 0,0 on the top layer
  8. Confirm it reads fffffe
  9. Pick the same pixel on the bottom layer
  10. Confirm it reads ffffff
  11. Add an alpha channel to the bottom layer
  12. Pick and inspect the same pixels on each layer again
  13. They should BOTH read as ffffff or fffffe

Expected result:

The color picker should show me the value of the pixel on the layer I'm picking, just like with no alpha channel.

Actual result:

The color picker shows the old value instead.

Edited by Jookia1