Yeah, I noticed that too. My own thought? Assembly crews had not yet popped the chamfered panels (those smooth edged panels seen in the corridors) into place upon the walls or laid all the floor plates into place before the ship had to "haul nacelle" to intercept V'ger.
But that idea may be negated in either "The Wrath of Khan" or "The Search for Spock". I'm pretty sure we saw the room briefly in those films, but I can't remember how it looked.