Debian GNU/Linux 9 is now available - from Trixie?!

[Rafał Lichwała]

Hi,

I've got Debian Trixie installed on three different machines (one laptop 
and two PCs) and on all of them there is the same strange issue:

Discover application (the one for app management under KDE Plasma) shows 
the green box (at the top of the app window) with text:

"Debian GNU/Linux 9 is now available." - with button "Upgrade Now" on 
the right.

Debian 9 is rather old release (I'm running Trixie right now!) and all 
the other packages are already updated.

What is going on here?

When I click this "Upgrade Now" button window popups with message: 
"Update Issue: There was an issue during the update or installation 
process. Please try again later." and "Show details" button says: 
"UpgradeSystem not supported by backend".

Anyone knows how to get rid of this strange behavior of Discover app and 
whay it is happening?

Regards,
Rafal