Flame Breath bugged interaction with Apocalypse?

If I understand these skills correctly, Apocalypse should gain glory from the use of Flame Breath, since it is dealing elemental damage. However, Apocalypse doesn't appear to be gaining any glory when that attack skill is used.

I don't think it has to do with being shapeshifted. When I use Rampage, the added fire damage from Walking Calamity is generating glory.

Is this the intended interaction, or is this bugged? It seems like a bug, unless Flame Breath is being treated as damage over time or not a 'hit'.