Repro steps:
1. Open attached project
2. Open scene "Test"
3. Select GameObject "Test" in the Hierarchy
4. Modify the "Text" field in "Test' script component
5. Enter Play Mode without pressing enter or losing focus of the input field

Expected: Modification isn't canceled
Actual: Modification of the string is canceled and the original string is outputted in the Console

Reproducible with: 2017.1.5f1, 2017.2.3p2, 2017.4.8f1, 2018.1.9f1, 2018.2.1f1, 2018.3.0a5

Notes:
- On Windows in versions: 2017.4.8f1, 2018.1.9f1, 2018.2.1f1 it only happens if you enter Play Mode with the shortcut (Ctrl+P/Cmnd+P)
- When you refocus the field in Play Mode the value reverts to the modified one