If you look closely, full absorption hearts in hardcore mode has a missing "wing" texture in it's right side as opposed to other hardcore mode hearts which has two "wings".
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Granted, that was resolved by a mod (in 2013), not mojang. Might be a good idea to let this run throught the process again, especially since every other hardcore heart does have both wings.

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It's different though?

This is included in that one.
they also appear to be asymmetric, as the marking only appears on the left half.

Duplicate of MC-41153, which is intended behaviour.