The actual effect:
These two images are have been saved one with the "Save color of transparent pixels" option, and one without. If you explore them
with the Pointer dialog, you will see that for the one saved without the option, the fully transparent pixels are R=G=B=0 (all other have a red component, even where their opacity is very low), while for the other all pixels have kept a red component, even the completely transparent ones.
These two images are have been saved one with the "Save color of transparent pixels" option, and one without. If you explore them
with the Pointer dialog, you will see that for the one saved without the option, the fully transparent pixels are R=G=B=0 (all other have a red component, even where their opacity is very low), while for the other all pixels have kept a red component, even the completely transparent ones.
PS: Hmmm There is possibly a bug there when saving high precision images. Will investigate later.