When updated packages are available, a notification appears telling that updates are available.  With apt or synaptic one can verify that this is the case.

Clicking on the notification icon or lauching muon updater from the console opens the muon updater window.

However this window is empty, just telling about the last time an update was made and suggesting check update. The window flikers a few times (as if it was trying to show something else). Tons of processes are spawned (> 20).

Clicking check for updates appears to do nothing (no progress bar appears, window stays fixed).

Weird enough pressing install installes the available updates, but again with no visual output.

Reproducible: Always