Bukkit

What steps will reproduce the problem?
1. Use a plugin that makes glowstone drop glowstone blocks instead of dust. What happens is that if a use breaks the glowstone the break event will be canceled, then the block will be set to air and the method to spawn item naturally will be used to spawn the glowstone block. There is thus no posibility for your plugin to detect that the glowstone was removed

2. As day passes to night the block will be set to glass, and the next night the block will be glowstone again... that we can remove and now we have a glowstone farm.

Suggestion:
Also check that the block really is there before replacing it. This way broken lamps will be detected anyways.