Im not sure if this has already been reported else where, or even helps, but I have a Surface Pro 3, and also have used a few distros of linux on it. So far I have tried 3 flavors of Ubuntu, Fedora, and Linux Mint ( Gnome, KDE, Cinnamon, and Xfce environments) and in all of those distros the latest release of Mypaint works 100% perfectly for me. The only function I could not use was the eraser button and right click; however that was because of Linux not having full compatibility with the surface pro...not an issue with Mypaint.
(Edit: Forgot to add, Ive noticed that when I run Mypaint in Win10, as soon as the application starts, I will have pressure sensitivity until I either lift the pen from the screen or press one of the buttons to pan the canvas. Again, not sure if that helps.)