There is a thing that causes this same symptom that I have found out by experience. If your battery is a little weak, or your battery cables are not very tight and not making very good connection, your bike will do the exact same thing. You will notice it starts up find when cold, but when you ride somewhere and stop. And then come back and try to restart, it will kick back and sometimes make a bad grinding noise from the starter area. This can be totally caused by what I mentioned above on our specific bikes. I also found out if you have a battery tender cable hooked on to your positive cable that runs down to your starter, then that can be enough to inhibit maximum voltage to your starter. Connect the battery tender to the second bolt on your battery posts and not the one that your battery cable is attached to. Before going on to the next possibility check these things out very thoroughly. Always keep your battery on a floating charger also to keep it up.