Items with the `end_cube` special model type do not show a glowing outline where expected

The easiest way to reproduce this is to download and apply the resource pack attached, hit yourself with a spectral arrow, then hold TNT and look at yourself. You will be highlighted, but the held TNT will not, which is incorrect and inconsistent with other held items.

You can also set glowing to true on item entities, item frames and item displays representing TNT and see the lack of outline in those cases, and equip TNT on your head or the head of some other entity via commands and make them glow too, noting a similar lack in outlining.

Expected result would be for the TNT item to be highlighted like the rest of the entity in question.