The bug:
Light emitting blocks and items have a special "glowing" visual effect when being held or placed on an item frame. However, certain items such as campfires don't do the same. See both pictures for a comparison (Education Edition items not included).
Notes: Items with the enchanted glint will glow on item frames, but not while dropped/in hand.
Update: Some glowing items were added after the creation of this report, I'll be adding them to the description:
Glows properly:
Small Amethyst Bud;
Medium Amethyst Bud;
Large Amethyst Bud;
Amethyst Cluster.
Should glow, but doesn't:
Glow Ink Sac;
Glow Item Frame;
Glow Berries;
Doesn't glow and might be intentional:
Amethyst Shard;
Spawn Glow Squid.
Can confirm on 1.18.0.27 beta. Also, I think the issue isn't just item frames. Items that (logically) should glow, like the glow ink sack, do not glow, even in your hand or dropped.