I don't have 11 to test. It may have to do with the autosizing available from the inspector.
Check out page 22 of the technical breif http://www.filemaker.com/products/filemaker-go/docs/techbrief_filemaker_go_121_en.pdf
Thank you for your post.
Does the top of the "box" touch the Header part? If so, the box becomes part of the header, and it will be cropped. Move the image directly into the appropriate part.
Any other information you can provide may be helpful.
It could just be the difference in how Go handles windows vs. how FMP Pro does. GO tends to scale the window down to show the entire layout while Pro will just show scroll bars. Thus, it is possible that the colored background appears to fully cover the layout in Pro but not in GO.
In any case, I would provide a non changing color backgrould by clicking the layout part's label while in layout mode and selecting a fill color. That's simpler than using a field for this purpose and should work identically in Pro and Go.