How to Reproduce:
1. Place an Oak Slab on the ground
2. Start flying
3. Set your position to be slightly above the Oak Slab, but still in the same block coordinates
4. Run the following command in chat and notice how it succeeds:

/execute if predicate {condition: "minecraft:entity_properties", entity: "this", predicate: {stepping_on: {block: {blocks: "minecraft:oak_slab"}}}} run say Test failed

This effects any blocks with a top face lower than a full block where the player can share the same block x/z coordinates (eg. Farm land, enchanting table, snow, etc.)

It also effects blocks such as the inside space of a door.