OK, so I redid all my setup and I think I found the "problem": Kaffeine (KDE 4) was also installed (must have done that at some point, although I can't think why. Old age...).
So the Kaffeine that was started automatically was not the same as the one I started from the TDE menu (!), which in turn explains why the programmation seemed to disappear.
Experiment running to check if I got it right this time
Thierry