I'm just now reporting this bug, but this started immediately with the DX11 update, and is reproducible 100% of the time. I have an old Windows 10 laptop that I use for boxing, and I have the habit of leaving EQ running at the character select screen and just closing the lid when I take a break. In Windows, I have "When I close the lid" set to "do nothing" while it is plugged in. (It is plugged in.) Prior to the DX11 update, this worked fine, and whenever I opened the lid the client was there waiting for me. Since the DX11 update things go like this: prior to closing the lid, EQ is full screen. After closing and re-opening the lid, EQ looks like it is in windowed mode (I can see the title bar at the top, and the task bar at the bottom), but if I move my mouse around the screen to hover over buttons, I can see that there's a significant offset between where my mouse is and where EQ thinks it is. Additionally, hitting alt+enter will change the client to actual windowed mode, where things work correctly again. (Hitting alt+enter a second time will change it back to correctly functioning full screen mode.)
You're seeing the full screen window while it's inactive. It changes to a restored window size and is inactive, and not hidden. If the first input is ALT+ENTER then you're also switching it to windowed mode.
Thank you for the response, but I don't think that's the whole story, or maybe I don't understand what you mean by inactive. If I press keyboard keys, like A and D to rotate the character, the character does rotate, so the window clearly has focus. Additionally if I alt+tab to another window and back again, EQ remains in the broken state with the mouse hover offset from where the mouse actually is. Also, I want to reiterate that this is new behavior since the DX11 update. It did not happen before that.