Gold coin duration upgrade seems broken, it just goes back to the standard 10 seconds when you leave the game and return until you buy another duration upgrade. Some achievements also act weird, I got the 10-bucket one automatically on returning (presumably for the 10-bucket you start out with) and never got "drop ten thousand balls" with over 100,000 dropped.
This is a nice premise and I'm curious to see where it goes in future versions!