Reproduction steps:
1. Open user attached Project
2. Press Play
3. Click "Keyboard"
4. Click in the middle of the screen
5. Hover on the left sidebar (A pin should appear under the cursor)
6. Press '+' ( '=' )
7. Exit Play mode
8. Enter Play mode
9. Repeat steps 3 through 6
Expected result: Another pin is added to the selection
Actual result: The Editor crashes
Reproducible with: 2019.4.27f1, 2020.3.9f1, 2021.1.8f1, 2021.2.0a17