If the author is here: it's easy to accidentally flip a card while trying to move it. Consider making flip be a more complex gesture, like a connect-click/long-press menu or a pop up confirmation.
There's a threshold that objects need to be dragged beyond to start moving, which is different for touch/mouse.
Also, what device/OS are you using?
It's not very often, but accidentally flipping a card just once is a very bad for a game.