@Popo. You leached 8 hp (50% of his remaining 15 hp), you did not actually go up to 8. The 5 hp you started with + the 8 you leeched was not enough to survive his 27 dmg tackle. If you had leeched, say, 50 hp, it would have displayed you going to zero, then added the 50 hp, then deducted the remaining damage.
While displayed in a funky way, the game is correct in showing a tie.
 "Monster Castle Defense"){kind=icon}
 "Five Minutes to Kill (Yourself)"){kind=icon}
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 "Bunny Invasion: Easter Special"){kind=icon}