Since many distributions switched to newer desktops like GNOME shell or Ubuntu Unity that do not feature system tray areas, where application tray icons can be shown, there are many user reports that Liferea seemingly doesn't start anymore.
This is very often because previously Liferea was started minimized to the tray icon and you clicked on the tray icon to raise the application Liferea window.
Different Desktop Behaviours
Well Ubuntu Unity just got rid of the system tray and tries to adapt applications to libindicate. When Liferea is compiled with libindicate support everything should be fine. If not it might "disappear" when "Start minimized to Tray" is enabled.
GNOME shell got rid of the system tray, but tries to be backwards compatible by displaying tray icons in the notifications area. In the default configuration the notifications can be shown by moving the mouse to the lower screen edge. When Liferea starts minimzed to tray you will find the tray icon there and can click it to raise Liferea.
Long Term Solution
The long term solution is a sad one: to remove tray icon support (starting with 1.11). But for the brave power users there will be an optional plugin to enable to restore simple tray support.
This workaround fixes the startup in all cases. Just run: