How to reproduce:
1. Open the attached project
2. Open the Level0 scene
3. Click Window > 2D > Tile palette
4. Select any Tile from the Tile Palette
5. Click Shift + [ to flip the Tile
6. Click anywhere to draw the Tile

Expected result: The Tile will draw in the flipped state
Actual result: The Tile will flip back to its original position

Reproducible with: 2021.1.0a1, 2021.1.2f1, 2021.2.0a12 (1.0.0)
Not reproducible with: 2019.4.23f1, 2020.3.2f1 (1.0.0)
Could not test with: 2018.4.33f1 (package errors)

Notes:
1. Issue does not reproduce if the Tilemap component is disabled
2. You can still draw rotated/flipped tiles until 2021.1.0a6 but the tiles from before the update will still be reverted to their identity position