No, I am not kidding you here.
I fed my Maskewraith a Fractured Seerus Mask Fragment and the little sucker just up and ate it.
For zero heat.
Was the fact they can eat the Mask Fragments a bug, or is the fact said fragments don't add heat the bug? It's confusing.
There's no bug here. Mask Fragments are a material. Sprites eat materials.
Any 1* material gives very little next-to-none heat. Fractured Fragmemts are 1*.
Seriously, try giving it ecto drops or light shards. It won't add any heat either.