Notification duration is not configurable (always 30 seconds)

Windows 10 Home x64 build 1903

I go to Settings app - Ease of Access - Display - Show notifications
for, and set it to 5 seconds or 5 minutes. This alters the following
registry item:

Key: Computer\HKEY_CURRENT_USER\Control Panel\Accessibility
Data item: MessageDuration
Data value: 5 or 300 (in seconds)

I even reboot the PC to make sure the registry change is effected
(rather than just signout of my Windows account although this is a HKCU
registry hive). Yet the toasts (popup notifications) are displayed for
30 seconds. I cannot get them to appear for shorter or longer
intervals.