McDonald's Cheeseburger Pricing is Strange...

I was recently going to get a double cheeseburger at McDonald's, and right before I ordered, I was checking the price.

340 yen for a double cheeseburger.

And a standard cheeseburger is... 140 yen?

Hold on, so if I get two cheeseburgers, it would be 280 yen total and I get an extra layer of buns too?

Confused by it, I ended up walking out with two standard cheeseburgers instead. I have either figured out the puzzle or I was missing something. Anyone?