Well, your landlord is certainly opening himself up to a number of issues by misrepresenting his occupancy. Whether you want to do anything about it would certainly be a decision to weigh carefully as it could potentially result in a move for you. Might be worth a free consultation with a local attorney to weigh your options. Legal advice never a bad idea when it comes to legal matters!
The legal burden lies on the property owner, not you. If the mortgage company finds out, they could demand payment of the loan in full. This could simply create a refinance situation for the property owner with no effect to your tenancy. Even if the lender takes a more serious approach, you did not break the law – he did.
As long as the landlord is living up this his end of the lease agreement, I personally would shut my eyes to the situation and let the chips fall as they may down the road. Meanwhile, enjoy the place that you are renting.