Following the reboot after installing a new application, I noticed that all of the icons in my Windows notification area (formerly “system tray”) were appearing in my taskbar rather than collapsing into the corner.

Somehow, the “Always show all icons and notifications on the taskbar” option was re-selected under Control Panel –> All Control Panel Items –> Notification Area Icons. (Note that you can also get here by right-clicking on the Start Button, selecting Properties, then clicking on the Customize… button on the Taskbar tab.)

Clearing this option restored my taskbar to its original configuration.