Reproduction steps:
1. Create a new Unity project
2. Enter Play Mode
3. While Editor is entering Play Mode, click on "Help" toolbar option
4. Wait until Play Mode starts and the window selection opens
5. Click on "About Unity" entry

Expected result: "About Unity" window is opened
Actual result: A tab from "Window" is opened ("UIElements Debugger" on 2019.4, "Animator" on 2020.1, "Test Runner" on 2020.2)

Reproducible with: 2019.4.3f1, 2019.4.4f1, 2020.1.0b13, 2020.1.0b17, 2020.2.0a15, 2020.2.0a18
Not reproducible with: 2018.4.26f1, 2019.4.2f1, 2020.1.0a1, 2020.1.0b12, 2020.2.0a1, 2020.2.0a14

Notes:
1. The issue does not reproduce on Mac
2. The issue seems to be only affecting "Window" and "Help" toolbars (all of their entries)