I find the Cabin an interesting thing and I believe it's well thought out, that the mysteries are not those that might be production errors and the like.
The thing is... the fact that Ben went to the cabin, but never talked to Jacob, combined with the fact that Richard knew that Jacob lived in the statue still, meaning since the time Jacob and Nemesis see the approaching ship, I sort of think that's not Jacob's cabin. Maybe it's Nemesis or who knows.
So why did Ilana and company go there expecting to find Jacob? Is it a portal of his... where yes he meets people? Then why would Richard not go there? If he was trapped there against his will (purpose of the ash line or whatever it was), why wouldn't have Richard known that, broke him free, or still think he was there?
As I think about it I suppose that he could have been imprisoned, and moved back to the statue after getting out, but why would the Richard and the others never have helped him get free? Do they know they don't serve Jacob? Is it not true that even if they think they do, they havn't?
And on top of this, Jacob WAS giving instructions this whole time, or at least, didn't deny it, so none of this makes sense? If he was willingly holed up in the cabin, why would he leave?
Basically, why did Ilana go to the cabin and not the statue given what she seems to know?