There are some minor mechanic problems with rengar

As you already know every time rengar ults a circle appears around rengar showing the range of his jump. Sometimes when I'm chasing down an enemy with my ult rengar wont jump on the enemy even though the enemy is barely inside the circle but clearly inside the none the less. Another problem with rengars ult is when I'm about to one shot my enemy with his one shot combo sometimes all my ability cast first and then I jump towards the enemy. I am not sure if this is a mechanic problem or if its just me because it happens sometimes when im about to attack from a bush.