I also suffered my first minor injury when I was preparing to end the session for the day... getting a mild rope burn on my wrist from the kite flipping on me unexpectedly when I was attempting to detach the lines from the bridle... Ouch!
I have a suggestion for setting up that will help you avoid the kite taking off unexpectedly.
Instead of installing the vertical spars and then attaching (or detaching) the lines as shown in the video tutorials, I always install the lines before putting in the spars, and take them out before detaching the lines. This way the kite cannot get any power to even try to get away from you and makes attaching the lines easier because you don't have to lift and hold up the sail against the wind.
Try it next time you are out. In my opinion it's an easier and safer way to set up.