I've included a small example demo attached to this.
Description of issue:
Prior to this main release (
20.1.47)
in your last service pack (19.4.48) the Ctrl+[Arrow Up / Arrow Down] would allow the user to go through a list quickly and select multiple items. If they did this keyboard nav on a checkbox listbox item that was not checked it would then check it, and if this keyboard nav was on checkbox listbox item that was checked it would then uncheck it.
You list in your docs that this is a valid keyboard interaction in the picture below, yet it's not working in 20.1.47: