Prius jerky sometimes?

I recently purchased Prius 2005 (~154K) and this is the first time i am using Prius. I have it for about 10 days now. I have not had any issues with it for the first 8 days but in last couple of days i have noticed a problem. When i am going a small downhill and stop at a stop sign with my foot on break trying to slow down. ( from speed of about 20 down to 0) i felt a jerk and that increased the speed a little bit and then i had to press break harder. I have see similar issue about 3 times now. All these incidents were while I am trying to slow down. The jerk is easily noticeable. I am not sure what is going on.
Is there any major issue with the car?