I've noticed you can place item frames on the same place, just by right clicking them on a fence. This was probably intended. Tho when i placed a shiny item (an enchanted item / nether star / Notch apple) in the first item frame , and placed an iron bar in the second (just by going inside of the first and right clicking), the iron bars also became shiny. I tried it with other items and yes, they got the shiny texture as well. (all the ones that aren't 3D in the
item frame , unlike ex: blocks )
I didn't try every item but i am quite sure they will become shiny.

I posted a lot of images so it's clear.