When using a background layer, switching to Indexed Color Mode fills all layer bounding rectangles with Color 0

[hsandt]

I added a Background layer (right-click > Convert To... > Background) to my project, made sure that my color palette had all used colors in it (including Background color and transparent color), then switched from RGB to Indexed Color Mode.

I noticed bounding rectangle of each layer being filled with the Color at position 0 in the palette.

To make it obvious, I created a MWE where it's a flashy green:

Using two layers, including a Background, underlined:

The original image:

Switching to Indexed Color Mode:

Workaround: move transparent color to Index 0 so bounding boxes are filled with transparency so nothing happens.

MWE

aseprite_MWE_switch_to_indexed_colored_mode_fills_all_rectangles_with_color0.zip

Notes

• If I delete the Background layer or convert it to a normal layer, there is no bug
• Effect is similar to Outline and convolution matrix tools create square border when transparent color index isn't 0 #3127 but action triggering it differs

Aseprite and System version

• Aseprite version: version number, installer/portable/Steam/beta/dev/commit-hash
• System: Windows/macOS/Linux, version, distribution

[Gasparoken]

Thanks for this report. I was able to reproduce it easily with the document you attached.