Problems when rolling back to previous Arduino AVR Boards version

[per1234]

Using Arduino IDE 1.8.6 Hourly Build 2018/09/06 04:33 with Windows 10 64 bit

1. Tools > Board > Boards Manager
2. Click on "Arduino AVR Boards" - It should show "version 1.6.22 INSTALLED".
3. From the dropdown menu, select 1.6.21.
4. Click "Install" - After installation finishes, it still shows "version 1.6.22 INSTALLED". Both version 1.6.22 and version 1.6.21 are missing from the dropdown menu.
5. Click "Close".
6. Tools > Board > Arduino/Genuino Uno
7. File > Preferences > Show verbose output during compilation
8. Sketch > Verify/Compile - the output shows the Arduino AVR Boards 1.6.21 core is being used, but with the Arduino Boards 1.6.22 toolchain. The same holds with uploads.

The problem does not occur with Arduino IDE 1.8.5.

Could this be related to Arduino AVR Boards 1.6.22 never having been released to https://downloads.arduino.cc/packages/package_index.json?