Reproduction steps:
1. Open the project "Input UIToolkit issue.zip"
2. Build and Run
3. Click the "Click me" button (see that the button works)
4. Press Alt + Tab
5. Press Alt + Tab or manually select the project's window
6. Click the "Click me" button

Expected result: the button is pressed
Actual result: the button cannot be pressed

Reproducible with: 1.1.0-pre.5 (2020.3.20f1), 1.3.0 (2020.3.31f1)
Not reproducible with: 1.0.0 (2020.3.20f1), 1.0.2 (2020.3.20f1)
Could not test with: 2019.4.36f1, 2021.2.16f1, 2022.1.0b12, 2022.2.0a8 (the button disappears when converting the project)

Notes:
- Reproducible on Windows, but not macOS (because Alt + Tab works a bit different)
- Could not reproduce the issue on a recreated project