Powered comparators won't change to the on-state texture, just the torches change texture.
That causes them to not emit any light when powered.
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Duplicate of MC-8776.
True with subtraction mode also.
Yup, But also in 13w05b
Ok guys, I downloaded the newest snapshot (two times cuz there was a crash bug) and the bug from this texture is still not fixed. Do something on it. (13w06a)
Note that they also fail to produce light. Spawn 150 and place it, and you have a "correct" powered comparator, which uses the right texture and produces light. This state of comparator does not occur in survival.

Hey everyone!
Please update "Affects Version/s:" to 13w07a and upvote this, it's still not fixed.
I'm glad I searched this because I've had the same problem. How am I supposed to see the texture of it I created in the game if it won't light up?
@Draven: Well, until this bug is fixed, you can preview it by giving yourself 150 ("/give yourname 150") and placing it. It's the currently unused, proper lit comparator.
Updated Version, still not fixed at 13w09b!
Thanks, hadn't noticed this. The comparators will not give off any light, though, due to the "on" state is stored in meta data instead of switching blocks.
Are comparators supposed to give off light, Jeb?
I think, seeing as the correct lit form of comparators exists as ID 150, and Jeb said the on state is metadata rather than switching to this block, it's likely intended. When comparators first came out, didn't they produce light? I'd imagine this was disabled due to the lag caused by comparator clocks - for the same reason redstone blocks do not produce light.
Confirmed, this also causes it to not emmit any light.