Reproduction steps:
1. Open the attached "1382173.zip" project
2. Open the "TMPBugScene" Scene
3. See the "Last Character Index: 13" message in the Console window
4. Select the "Text (TMP)" Game Object
5. Add the "-" character at the end of the "This is a test" Text in the "TextMeshPro - Text" Component in the Inspector window.
6. Observe the Console window

Expected result: "Last Character Index: 14" text message is shown
Actual result: "Last Character Index: 0" text message is shown

Reproducible with: 3.2.0-pre.1, 3.2.0-pre.2 (2019.4.31f1, 2020.3.23f1, 2021.2.2f1, 2022.1.0a15)