I ran into the same issue with MyPaint 1.0.0 64 bit on Windows 7 64 bit with the Monoprice (UC-Logic rebranded) TWA60. I can draw just fine with the tablet when pressure is disabled, but when I enable pen input (screen or window) the color history pops up under my pen and scrolls rapidly through the colors when I try to draw.

When I run the Input Device Test, x and y seem reasonable, pressure == 0.0000 always, the upper byte of state moves around a lot, and button is anything from 1 to about 14. The events with random buttons also spray the dialog output rather quickly compared to my working setup below. I'm guessing the rapid output is because of the way events are suppressed.

Gimp 2.8 also seems to exhibit similar behavior when pressure input is configured/enabled. While trying to draw on the image, context menus are flickering very rapidly under the cursor.

Sample output of Input Device Test with MyPaint 1.0.0 64 bit (which does not work correctly)

Out of frustration, I eventually tried MyPaint 0.9.1 32 bit. After overcoming some glitches with the Input Device Dialog, I was able to successfully get pressure sensitivity working. At some point I noticed that I had grabbed the 32 bit version of 0.9.1 (there was no 64 bit version available). On a hunch I tried the 32 bit version of 1.0.0. Success!

The output of Input Device Test with MyPaint 1.0.0 32 bit (which works correctly):

I tried to find a 32 bit version of Gimp 2.8 to confirm, but I couldn't find a 32 bit installer. Does gimp include both 32 bit and 64 bit libraries with their windows installer?

At some point while trying to debug, I tried running MyPaint on my Linux Mint install, and pressure sensitivity worked just fine. However, a different bug reared it's head and made it unusable (pen randomly going to x,0 0,y or 0,0 then jumping back to actual location).

Anyway, I have a feeling this is an alignment/size/structure packing GTK 64 bit Windows issue, but I hope this information helps.

Previous version of mypaint worked perfectly, but this version doesn't work at all. I can't use my tablet genius pensketck 9x12. When i start painting it starts switching colors, and doesn't allow me to draw the line. I get 4 squares with colors that are switching, and nothing else. Something is very wrong in this version. That is bug only related to mypaint 1.0.0 And 0.9.1 works just fine for me. Here is the screenshoot of a bug. I think it worked on linux the same for me.