edit: Solved. Not a bug.
I'm having some issues with ReaFir with the sound starting a bit before where it should.
steps to reproduce (in gif):
1: first render time selection without ReaFir. sounds starts where the MIDI note is. Ok.
2: activate ReaFir, with 4096 FFT size. Render time selection. Sound starts before MIDI note.
3: change FFT size to 32768. Sound starts even before. It seems it depends on the FFT size.
Is this expected? Or a bug? I'm not saying it is critically bad. Just curiousity.