I think it might be the way you are poping your jumps. I used to have very loose straps and could still jump and there are heaps of people jumping surfboards and skimboards strapless.
Perhaps you are letting the kite pull you upwards to much and not poping yourself upwind enough. Make sure you jump up wind with the board and that your back foot is the last to leave the water. the nose should almost point into the wind when you leave the water.
I hope this helps i am no expert but my advice is FREE.