Because its an X10 light... 
Did you click directly on the thread from the main screen, or did you click on the particular forum first? I did notice that clicking directly on a thread sometimes leaves the light on beside the forum in the main screen. I always click on the individual forum first and then the thread.
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"If you don't know what you're doing, do it neatly..."
I really don't know I have clicked about every thing there is to click and the darn thing is still on. I think someone wants us to always tink there is some geat new program out there we need as if we don't have enought already to keep us confused! 
Stuff like this just drives me nuts. 
