Cursor Moves Off The Page - Left Side Only

Can't move the cursor off the active screen to the top, right or bottom. But when I move the cursor to the left side, it goes forever.

I often do a split screen e.g. to look at two panels concurrently, you can go to the option between minimize & maximize (does this mode have a name???), move the panel to the right and you get a half-screen on the right. Do the same with another screen, move it to the left, and you again get a half-screen. Dunno what this feature is called, but it exists in Win7 & Windows 8, great for doing copy-and-paste from one to another.

Problem is, when I drag to the left, it goes off into space.