Reproduction steps:
1. Open the user's attached "UIToolkitUnfocusIssue-2021.2.zip" project
2. Open the "SampleScene" Scene and Enter the Play mode
3. Hover over the "Remove" button
4. Press the Enter key
5. "Button Clicked" and "Button removed" messages appear in the Console window
6. Press the enter key again
7. Observe the Console window

Expected result: No messages appear
Actual result: The "Button Clicked" message appears

Reproducible with: 1.0.0-preview.17, 1.0.0-preview.18 (2020.3.21f1, 2021.1.27f1), 1.0.0 (2021.2.1f1, 2022.1.0a13)
Couldn't test with: 1.0.0-preview.17, 1.0.0-preview.18 (2019.3.31f1) (UI Toolkit package not available)

Notes:
-To reproduce on 2020.3.21f1 and 2021.1.27f1 create a new project, import UI Toolkit package, recreate the UIDocument Game Object, replace Standalone Input Module Component with InputSystemUIInputModule, and import the assets from the original project