Reproduction steps:

1. Open "TilemapDeselected.zip" project
2. Open "Test" scene
3. Select "Tilemap B" as the "Active Tilemap" in the Tile Palette Window
4. Enter Playmode
6. Notice that "Other" scene was loaded
5. Notice that the "Active Tilemap" in the Tile Palette Window is set to "Tilemap C"
6. Exit Playmode
7. Notice that "Tilemap A" is the "Active Tilemap"

Expected Result: After exiting Playmode the "Active Tilemap" would reset to "Tilemap B"
Actual Result: After exiting Playmode the "Active Tilemap" resets to "Tilemap A"

Fixed in: 2019.2.0a6

Reproduced with: 2019.2.0a1, 2019.1.0a14, 2018.3.3f1, 2017.4.18f1