Here is the screenshot in its original form.

The story behind this is that during the Longhorn development process, Microsoft designers were toying with the idea of integrating what we know now as the Windows Sidebar into the taskbar itself.
To accommodate this, the taskbar became separated into two-levels where the application switcher was moved to a transparent row by itself on top. This freed up an incredible amount of screen real-estate on the taskbar itself which then could house Sidebar Tiles (as it was known at the time because each ‘gadget’ would dock as a rectangular tile).
The idea behind this was to avoid stealing another edge of the user’s valuable screen real-estate. Instead, it would have resulted in a fraction less vertical space but a more widescreen workspace which is more desirable.

Source: Istartedsomething