unused colors are automatically removed from palette for indexed image upon loading
Submitted by mor..@..hoo.de
found this while modding the classic game UFO: Enemy Unknown. I have a number of indexed-palette gif files, all using the same basic palette. However, when I open a file that doesn't actively use all of the colors, the palette shown by the "palette editor" dockable dialog only shows those used colors. ALL images do contain the full palette (confirmed in other image editors), but the GIMP automatically removes the unused colors from the active palette. (So if you try to copy parts of other images of the same batch, which use the same palette, into the current image, the colors end up black unless by chance they are also used in the current image.)
While palette reduction may make sense in some applications, it is definitely wrong in these indexed images. you are trying to work in a fixed "palette space", and all images need to retain the full palette in order to decently work with them.