Right so this has been modified about 10000 x as I read round the forum.
I'm running MyPaint 1.2.1 w64 on Windows 10 with a Wacom Cintiq 13HD and 2 Toshiba 32" Tv's as my other monitors. Latest drivers for tablet installed.
Been using Mypaint regularly up until about last september, always keeping the most up to date version. Never had any issues. Last september I rebuilt my PC and for many reasons, ended up having to upgrade to Windows 10. Mypaint working fine. At some point, it just... stopped. Didn't update anything. Looking back it was about the time I got my first monitor. Up to this point I had been using the tablet as my only monitor (my old one was not compatible with shiny new pc).
Since then, I have noticed two bugs. The first being the more annoying and the one I can't reproduce at will. Mypaint will be working fine, and then 'something' triggers it to go mental. Possibly my pan/scroll express key. Mypaint will draw fine with a mouse, but every time i use it with the pen, it will just constantly zoom in and out while drawing.
Today I installed the latest drivers for the tablet and the latest stable build of Mypaint. To begin with it drew perfectly well under mouse but when used with the pen, it drew a solid 2 inches to the left and an inch below my pen tip... All other functions as normal.
Sometime while typing a 'please help' post here we went back to zooming in and out every time my pen is in contact with the tablet screen. Still drawing 2 inches to the left and one inch down. Definitely did not press anything in Mypaint or any of my tablet express keys.
Just to note: pen and tablet functions fine with gimp, the entirety the adobe suite, and corel painter. I can use my pan/scroll key here and the function turns on and off just fine. I have seen a similar issue before with adobe Animate and the Wacom Intuos on the Macs at uni (don’t know models or OS). once again pen contact randomly caused the canvas to zoom in and out. This was fixed when resetting the tablet settings.
When doing the same here, my tablet only functions like an intuos without a restart. Must be noted that I have no issues when working like this. Calibration was fine. My pc wasnt recognising the tablet driver which is why it only worked as an intuos on one of my monitors. This didn't happen any of the other times I reset the tablet settings.
Restarted computer. Opened mypaint, accidentally pressed the pan/scroll express key. Back to zooming in and out. Must be noted did not get a chance to test functionality before accidentally pressing express key so may or may not be related. However, did not stop scrolling when I pressed the key again which normally turns off the feature.
Restarted computer, disabled my pan/scroll key. Now working as expected but calibration still off for each monitor. Same as before for the Cintiq display, now about an inch left on the one desktop screen when using as an intuos and about on inch left and two inches down on the other. Tested in Photoshop and no calibration issues there so definitely Mypaint related.
At this point I found this thread https://community.mypaint.org/t/mypaint-only-works-with-pen-on-multiple-monitors-if-win-10-is-set-for-the-same-scaling/574
Applied it. Calibration issues totally fixed! whoop! Thought I'd let you know however that this is still an issue. and also, unlike in that situation, my crosshairs etc stay perfectly under the pen tip at all times, it just draws in the wrong place. I have no issues when using the mouse even when scaling is different.
Still no idea whats going on with the zooming. Am apprehensive about testing my pan/scroll key theory as in the past resetting my device settings and/or restarting my pc have not fixed and I currently need Mypaint functioning for my latest uni project. Happy to test once project is over