Boulderfists "You cannot leech health" does not work

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What went wrong?
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boulderfist: https://i.imgur.com/u98r5yb.png

undisputed: https://i.imgur.com/pD1Snnn.png

“overkill leeched as health”. This should be ignored because of Boulderfists, but it is not working. whenever i use a strong skill like earthquake on a pack of weak mobs, it causes a lot of overkill and my health goes to full
Thanks!