Reverse speed no longer working (on a clip with posterize effect applied)

Hello,

I changed the frame rate to 1,2 (from 24FPS) of one clip in my sequence using posterize time effect. 

Now if I try to reverse the speed of the clip and it doesn't work properly. Do you have any idea why this is happening? As usually I'm right clicking the clip and click the reverse speed option. 

I'm including two screenshot of what it should be the same frame (same timeline position) one before and the other one after applying the posterize time effect (on a clip with reverse speed option activated)