Rendered Previews still render effects on each export

[Editor Jim]

I've rendered my sequence with Video Previews set to Apple ProRes 422.

I have a number of effects added to some of my video files - like noise and video posterize.

When I export with "match sequence settings" and "Use Previews" checked, my export still slows down on those clips with effects - as if they haven't been pre-rendered. 

 I"ve attached screen grabs.

What am I doing wrong?