Can use stained-glass to xray items in item frames

Note: Most noticeable for players using advanced storage systems.

Steps to replicate the issue:

Place a chest (or double chest) at eye level. Place an item frame on it and place in any stained glass block or pane. Only works on stained glass, not on regular glass.

Go 5 blocks behind the chest you have place and place another chest (or solid block) also at eye-level. Place an item frame on it facing the same direction as the first. It does not matter which direction (north, east, west, south) the two item frames are facing.

Place an item (like dyes) or a non-full block (like a lantern) in the item frame you have just placed (the second item frame).

Place a stained-glass block or pane in the first item frame.

If you look through the stained glass block or pane in the first item frame in the direction of the second item frame, you can see the item in the second item frame through the stained glass block or pane.

See images for demonstration.

Suspicions

It looks like this might be a part of the code allowing the stained glass blocks and panes to be transparent even while they are in an item frame. I uploaded an image of a stained glass block seeing an iron ingot through itself and through the item frame whereas the regular glass block does not do this.