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Light bleeds through BSP brushes

I made a simple house with only one door. Everything is made from a separate box brush, walls, floor, roof, ground.


But inside the house I see that the floor is lit near its edge. Everything is on grid and perfectly sealed.

Is this an engine bug or am I doing something wrong? Here, the map is attached.

Texture and material Dropbox - File Deleted

What happens is that the lightmap won’t align with where the walls are, so pixels from the outside can bleed to the inside, the best way to avoid the issue is to make the floor match the walls of the building.

But

. There is no air between walls and ground

I found the reason of this. Go in Settings - World Properties - Lightmass and set Indirect Lighting Smoothness from 1 to 0

That has nothing to do with it, the light hits the ground on the outside and the pixel extends beneath the wall onto the ground on the inside