Thanks Todd, figured it out. when I edit in an image file FCP normally creates an in & out (10 sec dur) in the center of the (source) clip but for reasons that are unclear, this img that was giving me a hard time had an “in” set right at the very beginning so there was no handle to sent a keyframe earlier than the In (in the Motion tab)
The other anomaly is that images normally auto-size to fill the screen, but occasionally they don’t or are stretched incorrectly.