@Ailurophile
You are correct.

Here's the problem with leech : when two blood puddles get put on top of one another, they don't "stack", they combine. It creates one blood puddle. So you walk into it, it counts as a single blood puddle.

Leech 'eats' the puddle as soon as you walk into it, though, so if you are standing there getting hit, it keeps trying to spawn blood under you (because you're bleeding or getting hit) but Leech is just instantly eating it.

So every single time the game adds blood under the character, they heal again (and remove the blood).