Keyframing problem with compound clip

Phew... Although I kind of hoped that I just did something wrong, I'm also relieved that I'm not yet totally senile.

Got a solution for you: Use an adjustment layer for the animation. FCP doesn't have one build in but you get free ones, eg. here: fcpxfree.com/products/adjustment-layer
An adjustment layer is basically an Apple Motion title effect with an empty title. You use the adjustment layer to apply effects over multiple clips at once so you don't have to apply the filter on all clips in a timeline separately.
And you can use the adjustment layer to animate the clips underneath it. So place your images in a timeline as you did. Now you can combine the single images into a compound for visual simplicity but you don't have to. Place the adjustment layer on top of either the single images or the compound of them and now animate the position of the adjustment layer NOT the clips underneath. Voila all will work as expected. And you can stay in FCP. Would be a shame to loose you to the dark side

Wow! Thank you, Carsten! I will definitely get check that out!