Rengar's Jump making him unable to cast abilities after jumping

I've been playing Rengar quite often in the past month, and I've been noticing that if you jump from a bush or from your ult, your abilities don't cast and you are unable to attack for about half a second after landing. The only way I have seen people assassinate squishies on the other team is when they use their abilities mid air. I've noticed this almost every game I play if I personally don't use my Rengar q mid air. Also, since Rengar is an assassin, and if you don't build tank, the half second you are unable to cast abilities means that the enemy is able to use zhonya's, dash, flash or any other escape mechanism before you do anything. Post if you have noticed this also, or if you have any tips on how to insta kill with Rengar, such as when to cast abilities in mid air to stop this from happening.