When tearing off a tab and dropping it into anything that isn't a Konsole window, a new Konsole window is created. So far so good. But when a tab is dropped into (the tabbar of) an existing Konsole window, another new window is created, too. I tested it with windows from the same Konsole process, the way it used to work.
I'm working on this this week, no need to worry.
*** This bug has been marked as a duplicate of bug 389897 ***
*** This bug has been marked as a duplicate of bug 403324 ***