Hi! is not a bug. Given that you can have more than one sprite opened at the same time, you have to select the sprite you want to change the settings to. So just click on the sprite you want to modify after moving the light.
I think i found instead a bug. Take a normal map, use the checkmark for alpha, so enable it. Now load a new image you can see the checkmark is still there but the alpha is not applied to use it you have to click to remove the mark and click again to enable. The program is great, mine are just suggestions like a whole parameter resets button that could help too.