When you wear sergeant's arid x pack and equip your scourn wings vanity u can still see the sergeant's arid x pack through the scourn wings. Ive also tried it on custom titantech to but it works fine. I haven't tried it on all back armors in the game yet just arid x, titantech, and battleshell so far ill get back on and test out some others even with my other toons see if any engi or op back armors mess up to.
Here is a pic of me wearing battleshell shoulders and scourn wings to show you that scourn wings completely cover the battleshell shoulders.
Edit: ok ive tested out some more back armors and it only seems to do this on lvl 25 shoulders (sandstorm, sunwalker, desert rat, and their platinum counterparts)
Here's sunwalker pack messing up
Here's desert rat pack messing up
The device that im playing on is a LG VM670 optimus v