In my experiences Developping VST efx ,
They dont use exact timing info about MIDI event within AudioBuffer.(=delta frame info)
All delta info is Zero , using Cubase as host !
(so maybe MIDI events like playing keyboard are push forward as Ha33y experienced)
But I checked StudioOne , delta frame info is propery stored !
then, I got great respect for presonus good job !
It is so strange , origin of VST didnt use their defined specification .
I heard that from Cubase SX , they didnt use delta frame info.