When you click to enter the mine, it brings up a screen that says Adjust the game difficulty. You can drag the slider up to how strong your character is, and the slider will stop. If you drag your finger across the screen (like if you could slide it to 100) and start a game, it will run at frightening speed. The visual slider stops, but the real slider needs to stop there too.
sorry but this is hard to explain, but do you know what I mean?
I've had this glitch too once, so I know what you mean! It's not really a big problem if you don't adjust it but yeah, they should fix it.. I've also noticed you get a LOT more experience (or whatever it's called) like this..