How to reproduce:
1. Open attached project "TileMap_NormalMap_Bug.zip" and scene "SampleScene"
2. Observe top white tiles having woodplank texture
3. Select Tile Palette's "Erase with active brush" mode, remove 4 wood tiles on the right
4. Observe top white tiles having dirt texture
5. Repeat steps 3 and 4 for all the dirt tiles on the bottom
6. Observe top white tiles having plain white texture

Expected result: the top sprites are always without normal map (should look just like in step 6)
Actual result: the white sprites (without bump map) sometimes copies random normal map from the scene sprites and applies/uses it

Reproducible with: 2019.3.0b4(7.0.1), 2020.1.0a7(7.1.2)
Could not test with: 2017.4/2018.4/2019.2 urp was not yet implemented