For some unexplained reason behavior now switched back to normal. I begin to suspect that this is some unstable cross application interaction between programs I have installed and 7TK that affects the windows task manager. In Any case, thank you for responding about this.

Many thanks for your quick response

You are right. Terminating 7TK did not resolve this issue :(

So I guess this is a system "feature", but now it is even more puzzling why you cannot reproduce it. Or why I have not noticed this earlier.

It this turns out to happen across the board (and not only to me), do you think 7TK can take control to avoid this misfortune behavior of the taskbar?