The trend in the states (and it's a good one, I feel) is to add more and more circuits, segregating loads better throughout the house. (The average kitchen in a new construction home, for instance, may potentially have 4 different recepticle circuits in it). This results in even new construction homes using the tandem breakers. No real problem with it, unless the electrician doesn't understand what he's doing (as this one apparently didn't). Still, wouldn't be a terrible thing to fix in this case, by just swapping the bottom 'A/C' leg and the GFCI one above it, and ganging the 'A/C' breakers together (like the breaker spaces below it for 'new heat').