Odd one this. I have a headless server, so access it via Remote Desktop Connection from other PCs. In MC standard view, the position of the mouse pointer doesn't match with where MC thinks it is pointing. So I position the mouse on an item and click, and an item several lines below is highlighted. It's aligned in the top left hand corner, but gets worse the further down and across you go. It's almost like the scaling /resolution of the mouse is different from the display.
Sounds like a Windows/driver/hardware issue? Maybe, but it gets weirder. MC pop out menus don't have the same problem, so if you can work out how to open the Tools menu, everything in it, and any lower level menus, all have correct mouse/display alignment. The Windows task bar at the bottom, and other non-MC stuff on screen is also correctly aligned. In Theater View, everything is OK. No other app exhibits the same issue. I've rebooted, checked the drivers, tried the usual stuff, but it won't go away. The client PC is in 4k resolution, but I don't get the same problem when connecting from a PC on a lower resolution.
MC26 v80, Windows 10 64 bit and drivers all up to date.
Edit: I just tried lowering the client resolution to 1080p, but had the same problem.