Thanks to AskLeo , I have found a solution at Kelly's Korner . Quoting him:
"Kelly Theriot, a Microsoft MVP, has a set of tweaks available at Kelly's Korner. They're fairly light on documentation, and perhaps even a bit techie if you want to understand them. On the tweaks page scroll down to item #240, and click on "Programs Aren't Minimized in the Taskbar". That will run, or download, a "vbs" (VBScript) program which will, after confirming, reset the Taskbar's properties. Note that several other aspects of the Taskbar will also be reset to their default states, but you should get your "running programs" area back."
Hope it works for you, as it did for me.
Best, Andre