MQTT add-on not shown as “Installed add-on” on the Supervisor Dashboard

I have installed the Mosquitto MQTT Broker add-on under Home Assistant Supervised.
After installation of the add-on I did not get a Notification from Home Assistant telling me that the add-on was discovered. However, the MQTT Broker was shown as a Device on the “Configuration - Devices” page, and it was shown as “Discovered” on the “Configuration - Integrations” page.
I could Configure the Broker from the Integrations page, and do the remaining setup like adding a specific Home Assistant User.
On the MQTT settings page I now can successfully publish and listen to messages, so it appears to be functional.
The strange thing however is that, even after a restart of Home Assistant Server, the add-on is not shown as “Installed Add-on” on the Supervisor Dashboard, and on the “Add-on Store” page the Add-on is not shown with a thick line above the field like the other installed add-ons.
Is this as expected, or is something gone wrong?

Well, to my surprise this issue solved itself.
Last night, which was 8 hours after the installation of the Mosquitto MQTT Broker add-on, the issue still persisted, even after several restarts of the Home Assistant Server.
But when I checked again this morning, 16 hours after the installation, it suddenly is showing up correctly as installed on the Supervisor Dashboard and the Add-on page.
So it is good that the problem (if it was a problem at all) is solved, but I am still curious about what caused this delay.
Anybody?