I installed DF fresh on my work computer (Steam edition), and I have an issue where the clock and system tray are shown on both sides at the same time.

I right-clicked on the second taskbar, disabled the Start Button, then disabled the system tray and clock (this was by accident, I just meant to hide the icons).
However the system tray and clock didn't disappear. They remained.

Then I went back and toggled it back to automatic, at which point they both appeared on the left side, while remaining on the right side.
They are both interactable (when not covered by the taskbar active windows).

I even turned off the clock completely, and both copies are still there.
See attachments.

EDIT: Toggling the Start Button to auto again causes a third copy of the clock to appear, and the Start Button overlapped it on the right side.

I finally got the layout I want by unloading and reloading the taskbar.