Update by Oval;
Items hold by other players show the item's default value. For example; Spruce Wood will look like Oak Wood as that's the default value; 0.
When holding the end stone brick walls, they seem fine. However, when another player is looking at you holding them, it looks like a cobblestone wall instead.
After I reconnected to the Realm, the texture seems fixed now. I had no texture packs enabled but after my friend switched items and back, the texture broke again.