How to reproduce:
1. Open the attached “IN-114389” project
2. In the Tile Palette window, switch from “AMap“ Tilemap to “ZMap“ Tilemap
3. Select a tile to paint with
4. Select the Default Brush
5. In the Scene window, paint some tiles
6. Save the changes
7. In the Tile Palette window, observe the selected Tilemap

Expected result: Selected Tilemap is “Zmap“
Actual result: Selected Tilemap is “Amap“

Reproducible with: 6000.0.5f1, 6000.0.58f1, 6000.2.5f1, 6000.3.0b2
Not reproducible with: 6000.0.4f1

Reproduced on: macOS 15.6 (M1)
Not reproduced on: No other environment tested

Note: It’s not consistent, so make more changes and save the Scene again if the issue does not reproduce