Windows 10 disable Aero Snapping
Solution 1:
Found it! The magic word is "Snap". The OS is Snapping the windows to the side, and then helpfully showing which windows to choose from. I've disable the "suggest companion windows" in Settings->System->Multitasking to fix it. http://www.tekrevue.com/tip/how-to-disable-snap-assist-windows-10/