Steem Monsters Vampire's Life Leech collision vs Goblin Shaman battle

Here is the screen from the battle: Death Splinter vs Fire Splinter:

here is the battle reproduction:

https://steemmonsters.com?battle=e2c172c6c492cd30ac9a56eae3aa37f3e9104564&ref=stepway174rus

The Goblin Shaman takes 1HP from each of Death Splinter team. The Vampire already have "1" so the system is such that can't reduce 1 to 0 and can't kill the Monster directly by Goblin Shaman's Ability.
BUT - when the Vampire tries to Leech the 1HP - it suddenly does not gained.

I can't check it futher, 'cos I've lost my Vampire and I play the Death Splinter enough rare and don't wanna to loose with such risky Vampire card 5 mana cost.