How to reproduce:
1. Open the attached project (1226069.zip)
2. In the Project window go to the Textures directory and select all textures
3. In the Inspector window enable the "Fadeout Mip Maps" option under the "Advanced" dropdown
4. Select the "Aniso Level" value input field
5. Press Ctrl+Z to undo
6. Press anywhere on the "Aniso Level" value slider

Expected result: The "Aniso Level" value input field displays a numeric value
Actual result: The "Aniso Level" value input field displays "<multi>"

Reproducible with: 2017.4.38f1, 2018.4.19f1, 2019.3.6f1, 2020.1.0b2, 2020.2.0a3

Notes:
1. Deselecting the "Aniso Level" value input field or applying any changes made to the textures sets the value to a number
2. Tested on Windows 10, Windows 7, Linux(KDE Neon 5.18) PC's and a Mac