Your down payment doesn't come out for renewals, but your monthly fee does increase to make up for the difference.
You do know if what the OP was true, Mickey would show up at your door with a crow bar demanding that extra payment. Its like the beer price, then they add tax on top of the price. Who does that? Have you ever been to a bar that adds tax AFTER the price of the beer? Most places, the beer is $5, you pay $5. Not Disney. Its $7, plus another 60 cents.