Add/Remove Applications calls itself "synaptic" in authentication alert
Binary package hint: gnome-app-install
1. Clear your passphrase cache if it is not already cleared.
2. Start Add/Remove Applications, and choose an application to install.
3. Click "Apply" and "Apply".
What you see: "Enter your password to perform administrative tasks - The application 'Synaptic Package Manager' lets you modify essential parts of your system."
What you should see: Something that doesn't mention "Synaptic", because you're not (knowingly) using any program by that name.