How do I get lost windows back?

[hw]

Hi,

my konsole window has disappeared or has become invisible or is
somewhere outside of the display (if that is possible).

It doesn't show up when pressing Alt+Tab and not in the overview of
all windows.  According to 'ps xca | grep kons', konsole is still
running.  When I open another konsole, the new window is titled
'Konsole <2>'.

Why does this happen[1], how can I prevent it from happening, and how
do I get the lost window back?


[1]: I think I moved it into the top left corner to see if it would be
maximised and/or get tiled and then it somehow disappeared.  In System
Settings-->Workspace Behaviour-->Screen Edges, both options were
enabled at the same time by default.  That doesn't seem to make sense,
and I turned the Maximizing off.

BTW, what is the behavior 'Remain active when windows are fullscreen'
supposed to do?  Deactivating windows once they're fullscreen doesn't
make sense.  What is remaining active, or does not remain active?  If
it's a behaviour that remains active or not, then I can only say that
activating or deactivating an unknown behaviour isn't exactly helpful.