But when I try to move it back (3D view --> "Display in same Window") the program always stalls, i.e. it becomes non-reactive. The menu bar gets grayed out. When I change window size it does not get redrawn, it hangs and is simply dead!
The only way to "re-animate" things is killing it via the Windows task manager and restart the program. But apparently it memorizes the fact that the 3D view was popped out and re-opens it again in a separate window right after restart. And if one tries to move it back to the home windows it hangs again! Start-over!
So, do I how have to live with two windows from now on? What can I do to get that 3D Windows back into the main window gracefully?