Extra unwanted fades on timeline stills with opacity fades via handles

I'm doing a lot of manual handle fades for dips to black etc., and many clips (stills at the moment) are flickering up and down between the handles where there is no fade. Strangely, when I adust either handle at all, it corrects the problem, but it keeps happening frequently, not good.

Wondering if it could have to do with my using "Paste Effects" to use the same in / out timing. When doing, I'm not pasting any other effect. After pasting, the handes appear adjusted as desired, and I'm pretty sure this hasn't happened on all clips with pasted fades.

One strange thing: one still with collor correction would also lose the flicker when I deselected the color effect in the inspector, reselect and it came back. But most of the clips in question have no effects on them at all.

I have trashed preferences, no change. Out of ideas. Anybody? Thanks.