Light is causing my decals to light up when they should not, how do I fix this?

I noticed that some decals I’m using, after building lighting, create “lit” decals on the other side of the wall as if the light has leaked through the decal itself to cause it to light up on the other side of a wall, even though there are no holes in the mesh. It is like the decal is lit up yet at the same time it is not a light source. Is there a way to fix this so the light no longer leaks through decals? The decals themselves do not emit any light, they are normal damage decals. The decals that are in the shade/shadows, do not seem to be lit up like this.