Herald of Blood explosion not working in Wyvern form

I'm playing around with a blood mage wyvern. I have bleed being applied by my Rend ability. I can see the blood loss being applied as a result. If the enemy dies while I am in wyvern form, there is no explosion. If I switch to human form before the enemy dies, however, even after applying the bleed while in wyvern form, the explosion *does* happen. To me this is a bug as I don't see any text in either Herald of Blood or wyvern form that implies this will not apply in this scenario.

Herald of Blood does say it needs a martial weapon, but the talisman is indicated in the martial weapon list. And as mentioned, I can see the blood loss animation being applied properly here, the only issue is with the explosion.

Edit: So I noticed today after reworking my build a bit that the explosion from Herald of Blood has actually flipped somehow. Now I can't trigger in human form, but I *can* trigger in Wyvern form. I'm not sure what has changed here and I haven't been able to get it to flip back or work in human form since.