When using the damage_sensor component with the has_damage filter compared against "fatal", any event associated with this filter will fire immediately (regardless of health)  if any damage is taken by the entity from the following blocks:

Sweet Berry Bush
Magma Block
Cactus

The filter behaved normally when used with the following damage blocks:
Campfire (both kinds)
Wither Rose

"minecraft:damage_sensor": {
	"triggers": [
		{
			"deals_damage": false,
			"on_damage": {
				"filters": {
					"test": "has_damage",
					"value": "fatal"
				},
				"event": "minecraft:event_to_run",
				"target": "self"
			}
		}
	]
}

These are not exhaustive lists. Tested on Windows 10 PC and Xbox

Steps to Reproduce:

1. Load a world with the attached Bug Test add-on.
2. Create a horizontal pad using one of the following blocks: Sweet Berry Bush, Magma Block, Cactus (see attached image).
3. Summon a Zombie Pigman onto the blocks (no event required).

Observed Results:

The event associated with the has_damage/fatal executes immediately.

• In the case with the attached add-on, the event creates an explosion.

Expected Results:

Damage should be take from the block, and the fatal damage event should only fire when the entity health value crosses zero.

/Edit: I've attached an image of the blocks used, an add-on with an entity configured to demonstrate the bug, and updated the description accordingly.