The "Updates" applet shows that 1 package can be updated. However, neither Muon updater nor "apt-get dist-upgrade" can update anything. I have this problem on one of my systems and not the others. Reboot or "apt-get update" doesn't help. Reproducible: Always Steps to Reproduce: I'm not sure what steps are needed to reproduce this. It simply started happening after some update. Kubuntu 15.04, x86_64, KDE Framework 5.3 installed from Kubuntu backports.
Created attachment 92512 [details] A screenshot showing the problem
Correction: a reboot did help with the applet. I thought I'd rebooted the system earlier but apparently I didn't.
It seems the problem happens after updates are installed. The applet doesn't update its number of packages that can be updated after the update.
*** This bug has been marked as a duplicate of bug 347602 ***
My experience is that I'll see notification that 6 packages will be updated and 3 are security updates. I open muon updater and 3 system updates are listed, but no security updates are shown with no way to choose not to update them. I click update and muon d'loads and installs 6 packages.