In Windows 8.1, when you move a window to the edge of the screen, it "snaps" into full screen mode (or fills the screen from top-to-bottom). This behaviour can be turned off.
My computer "Desktop" is almost always full (and then some). (Right now (and this a light day), the Desktop windows include: 6 Firefox browsers, 4 Directory Listings, 2 PDF/Acrobat files, 1 Notepad++ window (with 3 text-type documents open in tabs), 7 LibreOffice documents, 3 Outlook windows, and the Control Panel). In order to view and use the various windows, I rearrange things frequently, shuffling them aside, minimizing, and resizing things, to view windows the windows as needed.
The "snap" feature in Windows 8.1 makes rearranging things (to my liking) difficult. When I try to move a window aside (to see one below), the window snaps to a larger size - somewhat defeating my intention- when I'm trying to see a window beneath the one being moved. If fact, it's down right antagonizing.
It can be turned off (thank you, very much, and so glad your gone), as follows:
Control Panel\Ease of Access\Ease of Access Center\Make the mouse easier to use
Make it easier to manage windows
Check the box:
Prevent windows from being atomatically arranged when moved to the edge of the screen.