After drawing on the tablet for even just a moment, the mouse stops working for 5-10 seconds before it will re-engage. I am using the latest (at this time) version of Krita 3.3.2 on Windows 8 (not 8.1). I have a Tooya Pro tablet, and Logitech G700s mouse, with an HP Pavilion G7 2722NR laptop. In Wintab mode, the tablet works perfectly. The mouse will work until I start drawing on the tablet, even for just a second, and then mouse movement and left/right buttons will no longer work, but will re-engage after 5-10 seconds of keeping the pen away from the tablet. The mouse is not totally disengaged from the system, and the 4 thumb buttons still work. One button I use for 'E' for toggling eraser mode, and it continues to work, despite the mouse not moving, and not being able to click or right click. When switching to Win8 + Pointer mode, the mouse works normally, but the tablet function fails. The pointer continues to move normally, but regardless of pressure nothing prints to canvas. If I tab out of Krita quickly to any other application, mouse function re-engages immediately. I am not able to replicate this behavior in GIMP, Photoshop or Inkscape. I tested this on all versions of Krita from 3.0.1 on, and it exists in each. This behavior does NOT occur on version 2.8-2.9, and both mouse and tablet function exactly as expected. This is exclusive to Krita 3.0.0+ I have not yet tested this on Linux on the same machine, but will later and add that information here.
Also wanted to note that the mousewheel also DOES work when the mouse and left/right buttons do not work.
Please make a tablet log: https://docs.krita.org/KritaFAQ#What_if_your_tablet_is_not_recognized_by_Krita.3F -- that will show us whether we get mouse events at all. Whether or not other applications work is not really relevant, since they are written with different toolkits. And Krita 2.x was written with the previous version of Qt, which was rather different as well. And it's, obviously, something specific to your setup since otherwise other people would have complained before.
I am left handed, but use my mouse with my right, so I'm using both in tandem, so it's very apparent to me. But for many people that do not use their mouse at all when they are using the tablet, this bug could go completely unnoticed, simply because there's no interaction with the mouse. That being said, you are probably right. My mouse-tablet combination works on every piece of software, including the previous versions of Krita, but it's probably my setup and has nothing to do with the one thing that it doesn't work with. That's the logical conclusion.