I've made a few pages etc so surprised I can't fix this on my own.
I'm making a simple image gallery. All roll-over.
As you can see, the image in the over state always falls below the thumbs.
I can't change it in layers etc, presumably because it is part of a component?
It was just supposed to be a quick thing :Q!
The 'layer' needing to be moved was the button, not the image in the over state.. duh!