Dual-Monitor causes mouse DPI increase. It's not a game breaking bug, just one to add to the list.
Setup:
Monitor 1: 1080p (1920x1080)
Monitor 2: 4k (3840x2160)
Mode: Mirrored (1080p Primary)
Bug: Mouse movement speed becomes twice as fast as desktop, and the size of the mouse icon doubles. I suspect something is happening with scaling, but I can't be sure. (Bug is present in vanilla and modded)
Reproduce: Any time I attach the HDMI for the 4k monitor while the game is CLOSED, the bug does NOT occur. I can launch the game, load a save, and then connect the HDMI with no change to mouse speed or pointer size. If at any time I alt-tab or otherwise minimize the game window, then return to the game, the bug does occur.
Fix: Close the game, disconnect the HDMI cable, relaunch the game, reconnect the HDMI cable. (Optional:
Summary: Its a minor bug to be sure, but those with less technical backgrounds may find the sudden double-movement speed of the mouse to be unplayable and refund. We definitely want to prevent that. I can provide a short screen cap or other data if requested, such as a DXDIAG.