I'll keep at it when you leave the cave it saves so not sure why it keeps spawning it for you.
if you reload does it respawn it could be my last fix. fixed the saving but you needed to collect it once more to actually save the data.
think i found it or at least something related, dieing and respawning was not saving data so if you went into the cave solved the puzzle and died you could collect the ember heart and puzzle would reset same for the moth mine.
also if you have lit all the fires you can ditch all your ember hearts in igni then save and exit his inventory slot is not saved currently.
