Bug in minion revive timer reduction

How is it that when I take up the nodes for faster revive of minions (resulting in a total of 50% faster revive speed) actually brings the revive timer down to 4 seconds revive timer. But as soon as i get more revive speed (100% or more), the timer doesn't go down below the 4 seconds????

Is there a hard cap on revive timer? and if so, WHY???? GGG, minions are supposed to be able to protect you, not leave you vulnerable for 4 entire seconds? Why even have items which speed up revive timer in the game if this is not even possible...