I'm having trouble figuring out exactly when this "kick back" is happening.
Are you saying that if you push the kick starter lever down with your flip-flops and then your foot slips off, the lever rapidly snaps back up to the top?
If so, that is just the return spring doing its job.
It shouldn't damage anything but try to keep your foot on the starter lever.
If your saying you try to start the engine by just walking up to the motorcycle, flipping the lever out and then stomping on it and then, half way thru the stomp it suddenly stops causing your foot to come off and the lever then snaps back up to the top, you are using the wrong method of kick starting.
The reason the lever stopped is because the piston started up on the compression stroke and the force of the compression stopped the progress.
If you push the kickstarter lever down slowly until it stops moving, and then you apply more pressure to the lever to overcome the compression, the piston will slowly move up in the cylinder as the compression escapes.
When the piston reaches the top of the compression stroke, it will suddenly become very easy to move the kick starter. At this point, stop moving the kick starter down.
Allow the kick starter lever to return to its position at the top of its stroke.
Then, with the piston just past top dead center, give the kick starter a full kick all the way to the bottom of its stroke.
If you are doing this and bringing the piston to TDC before you start the final, full stroke kick and the engine suddenly fires, driving the kick starter lever back up, the ignition timing is set too far advanced.
There is no easy way for you to fix this yourself so take the motorcycle to a shop and tell them in detail about what starting method your using (piston to TDC, then kick) and tell them it is kicking back.
They should be able to fix the problem.
If the engine is actually firing too soon and kicking back this will rapidly destroy your starter sprag clutch. Get it fixed as soon as possible.
I the meantime, assuming the engine does not try to kick back during starting when the electric starter motor is used, stop kick starting it. Use the electric starter until it is fixed.