I too have this, very troublesome. Single monitor, permanently attached to my desktop computer. Windows 7. Direct X 12 option.
Side comment if you go into the Services.msc and restart the Desktop Window Manager after launching the game it will restore the aero desktop scheme. Until next time you launch the game of course.
WoW and my system were running absolutely fine previously so YES please to a configuration option to disable this intended change, ASAP!