@haakon, I believe any iOS8 devices will always take priority in reading .nib files over Launch Images and that's the Apple's way of how the OS behaves.
I took a brief look at your .zip file.... I'm not sure if this approach would help, but you can try building the launch screen by piecing the elements together in Interface Builder.
a ) Set a tiling / bleeding background for your splash's background
b ) Set 3 floating images that represents 1. Game Title , 2. Main (centered) Character, 3. Company / Publisher Logo
c ) With the proper constrains, let them float and position dynamically
The way I'm seeing this (could be wrong) is that the launch image set cannot pull the perfect static image dynamically and displaying/behaving like the old launch images.
But if we take a different approach similar to building web/html layouts, and start layering each display elements relative to the display, then I think you can achieve the perfect result:
a ) Create a tiling background that bleeds out of screen, so wider displays (iPad vs iPhone) can make use of it
b ) Create a floating title image, center aligned, stays at the top of screen
c ) Create a floating character image, center aligned, stays center of screen
d ) Create a floating footer image, center aligned, stays at the bottom of screen
Hope this helps! Or at least hope this can give you an alternative solution in troubleshooting the problems.