Perhaps I missed the memo but are we allowed to still purchase horse and dog tickets each month? When both of my sets expire I purchase horse tickets and then go to purchase dog tickets and it gives me the error of "you've already purchased this month."

If you have tickets from last month you didn't use, it won't let you buy more until you use the last months. It's a bug Sam has to correct. So if you have them just use them, then you should be able to buy more.