It kind of sounds to me like the "normal" Kohler kick back. If you read the starting instructions, they tell you to pull until you feel the compression stroke, pull carefully through it, and then pull to start it (or something along that line). When I bought the machine, my dealer explained to me to be careful with the starting procedure.
We have a 14hp Kohler on our Exmark 48", you are describing exactly how it starts, and I will never buy another one until they develope a real compression release. The kick back can pull you back over the machine if you are not ready for it. For all the guys who run Kohlers but have electric start, you may not have experienced this. This is the biggest of a bunch of reasons why I hate our 14hp Kohler (others include: poor air filter design, runs rough, loud, governer responds slowly). Yes, the engine runs and does it's job, it just doesn't compare to our other equipment that runs all Kawasaki.
Maybe I'll give the synthetic oil a try, I had never heard about that.