I can't remember the name of the setting that allows new windows to be added to the existing one as a tab, but when you do use this wonderful feature, (so say you type Ctrl+E, rather than a new window, it opens a new tab in the existing window of tabs) - it's not working for start menu search bar "see more results" windows. It just doesn't follow through, though the windows explorer window is activated.
I'm sure it's not too complicated to fix as Control Panel and all other types of windows explorer windows appear to be fine. hope you can fix it for the next update!
sorry, I meant Win+E, obviously.