Silly me !
I have a four button mouse. Now, I have just arrived to the Linux world from Windows. In windows I always double click using my fourth mouse button when opening directories. I took this habit whith me into Linux. And in Konqueror this mouse clicking resulted in directories opening up in new windows.
An ordinary left doubleclick in Konqueror results in directories opens up in the same window, just as I want to.
So, the force of habit is strong.