The beacon beam can travel through some blocks, (non-solid mainly), whereas it is stopped by solid blocks.
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kumasasa
Those blocks are "transparent" for the game
Light and the beam can pass through these 'transparent' blocks.
This is normal.
Yes, but the piston? The chest?
Yes, the game considers them transparent.
kumasasa
Every block which is not 1x1x1 blocks large is "transparent", read on here http://www.minecraftwiki.net/wiki/Opacity
(Note that extended pistons are not full blocks, and retracted ones are technically the same block.)