On windows I open documents by dropping them on titlebar (most upper part) of window of other opened documents. And they open ok.
But on Linux with KDE I can not drop document on upper part of window. When I drop on middle of window, it creates section.
Please, repost this bug to KDE team, if needed.
When dropping the document on the start center, it opens it, but indeed on any platform dropping it into an existing document inserts it as a section (by design).
This is not our bug as this should be handled by the window management system.