I couldn't find anywhere to file a CodeXL bug report so I'll put it down here.
Create an Array texture
Create a Framebuffer object
Attach layer of array texture to framebuffer.
Render to framebuffer.
This does not update the image of the texture in CodeXL. I spent about a day thinking either my driver or code was broken, but actually, if you click on the texture, select the correct layer using CodeXL, and then click data view and back to image view, the image will be displayed. I guess that the layer slider is not causing the image to be redrawn.