Spaces won't let me drag a space to another space

I’m running the latest version on Mountain Lion
I’ve used TotalSpaces on previous versions of OS X too.
I’ve never been able to drag a window to a new space. Well, shouldn’t say never. It works. Rarely and for no apparent reason.
I run Firefox in space 3. If I try to drag it to space 2 it stops when the cursor stops on screen edge.
Obviously, I’m doing something wrong: anyone help me out?

On TotalSpaces v1 (which you should be using on Mountain Lion) then dragging should indeed work.
But on v2 it will only work left and right, not up an down due to limitations with what I could do with OSX10.9 and 10.10.

However, as I said, on OS X 10.8 it should work. However, the mechanism is different depending on whether you are dragging left/right or up/down. Which directions do you have problems with?