I think this encourages people to check in often, and not make extra houses to cash in on coin collecting. Plus, this gives everybody an opportunity to make more friends in the game! Overall, if you check in regularly, you should be just fine to make a bunch of santa coins when you have all the houses. Plus, I think EA…
If you want to prevent this, press the Minus symbol on the top right of each house's pop-up box. You'll be able to prevent from switching to one or the other. I made this mistake yesterday too, but if you keep yourself aware, and "lock" changes to the houses you should be ok.
The sooner you build up your houses with decorations, the sooner you can get items. If you want to get a jump on the Mapple Store and Barney's Bowlarama, this is the way to do it. I am getting near 100 coins a day with Santa's Village, 3 friends and collecting from houses. Do it!