Disable multiple workspaces?

[WanderingPhilosopher]

I have Mac OS X El Capitan (10.11.5) running on a Mac Mini (late 2009).

I don't know how or when, but somehow I've managed to activate multiple workspaces. I've let it go for quite a while, but it's very annoying so have decided to try to tackle the problem. I don't know why or how it's happening or how to make it stop. Google hasn't yielded a useful answer so far. I unchecked everything in the Mission Control pane of System Preferences, logged out and back in, and that doesn't seem to have helped.

Can anyone let me know what might be going on and how to stop it? Perhaps one day I'll want multiple spaces, but for the moment I do not, and I don't know how to control them. I think it may be slowing things down, but at the very least it's inconvenient not to be able to overlay the calculator app where I need it! (For some reason I automatically switch workspaces when launching it.)

TIA for any help.

 

[Floris]

If you go to expose overview, you can see the top having the multiple windows.
You go fullscreen, it puts it in a second workspace.
If you hover over it in the top the x shows up and you can delete it.

It's there now, you can't turn it off.

And with a key combination and dragging the mouse up hard.. you can push an app to another workspace.