How to reproduce:
1. Open "TilePalette" Unity project
2. Open Tile Palette window
3. Drag some sprites into the Pallete
4. Press Ctrl + z to make Undo
--All dragged sprites disappear
5. Drag one more sprite to the palette
6. All previous sprites in tile palette appear but not last because it's deleted with undo

Expected result: When pressed Ctrl+z only the last sprite from palette should disappear
Actual result: All sprites become invisible but only last is removed

Reproducible with:2018.2.0a5, 2018.1.0b11, 2017.3.2f1, 2017.2.2p1

Note:
2018.2.0a5 cannot add new sprites to the Tile Palette
2017.2.2p1 undo is not working at all
2017.1.3p2 doesn't have Tile Palette