Windowed (Fullscreen) no longer working?

I play on Windowed (Fullscreen) mode. Since update 42, it seems that it no longer works as windowed mode, like before, but rather as fullscreen mode. So every time I alt-tab, or physically adjust the volume on my external speakers (which activates the on-screen volume overlay), it seems to turn off and reset my monitor. Tabbing between ESO and other applications results in my monitor turning off (going completely black) for 5-6 seconds, similar to what happens when you change the resolution. The game is still running as normal throughout all this. It's not game-breaking, but it is incredibly frustrating as I tab out often to check TTC prices and furnishing selections. (Edit: I know about the Environmental Sustainability changes and it's not that. I've disabled them in any case.)