A particular light in a German aquarium kept short-circuiting and no one could figure out why. Using camera surveillance it was finally discovered that every night, the octopus would climb to the edge of his tank and shoot a jet of water on the light, shorting it. It was speculated that the light had been bothering the octopus' nocturnal routine.
Let's not attribute any aspect of his behaviour to the crippling reality of captivity. Oh, no.
That seems to support the previous posters theory.
So let's move the light further away, but keep it on, because it suits us to keep it on when he's sleeping =(.
Poor little guy. sigh