The Pantheon Desktop Environment packages are installed in Sparky from a 3rd party repositories.
The latest upgrade has broken the desktop on Sparky 5.x based on Debian testing “Buster”.
The desktop packages are targeted to Debian Stretch and still work fine on Sparky 4.x.
So, I removed Pantheon desktop installation from MinimalGUI/CLI iso images, and blocked installation via APTus on Sparky 5.
Also added Slim display manager which (temporary ?) replaces Lightdm in the default installation.
Make sure, that a 3rd party packages are not built by Debian devs or me.
Installation of the Pantheon desktop can be done on Sparky 4.x via ‘sparky-aptus’ => 0.3.x with the latest version of ‘sparky-desktop’ => 20170902.