Continuum motion blur not working properly

I am using sony vegas 20 and when I add motion blur to a video with a velocity envelope every time the clip slows down it flickers black and ruins the video. Anyone know what the problem is and how to fix it ?

Hi, I see that, I tried it on an MP4 but quickly swapped to a ProRes 30p clip as that works much better in VP 20.
The first velocity keyframe is Normal 100 speed, second keyframe is 220, the third is 34, everything works fine, but if I change that last keyframe lower to 32 it starts flickering on the later part of the clip, I struggled to get it at 33.
Sorry I’m just sharing what i see but 33 is 1/3 if that has anything to do with it :man_shrugging: