Delay rendering xp orbs when being dropped

As for minecraft 1.5.1 and above there is some delay at rendering xp orbs when they are being dropped by mobs, xp bottles, furnaces, and any other thing that gives xp orbs. This delay was not in the game when xp was introduced and is kinda weird dont see the orbs when you kill the mobs

PD: In the very bad quality videos, see the MC Version
PD2: the F3 is activated