/damage returns a positive result for a Sulfur Cube even if it's not damaged

When a Sulfur Cube does not contain a block, using the /damage command applies damage.

When it does contain a block, using certain damage types with /damage returns the “Applied damage to Sulfur Cube” message, even if it was not damaged. Several types of damage still do apply damage but for those that don’t the returned message is still positive.

Expected Result: For the Sulfur Cube to not get damaged, and a message similar to the existing “Target is invulnerable to the given damage type” message to get shown.

Actual Result: The “Applied damage” message is returned, with no damage actually applied.