User blog comment:Scooter8pie/Transparency Bug/@comment-4583259-20111108165227/@comment-4583259-20111110032949

I myself noticed it while illuminating surface features (like the entrance to an underground tunnel, which I typically mark with lights in a distinctive way). It is fairly common to leave a trail as you walk so you can re-trace your steps. In this game (versus Minecraft) you have no way of re-spawning to your start location, so leaving a trail is more important.

In Creative mode everything is free, so you can drop tons of lights while you walk and never run out. Maybe that's what Scooter8pie was doing.