My mouse's x-position seems to be dividing itself by three-fifths and I'm not sure why. This has been happening whenever I drag an icon, drag a bit of text or image out of a browser window, or even engaging the click-to-drag Yoke Controls in the FlightGear flight simulator (the mouse button isn't even depressed during that!).
xinput test-xi2 --root based off another post I've seen, and discovered
event: 1006.60/795.00 immediately becomes
event: 402.00/795.00 etc... Though it seems to be happening in the very same event, as the valuators in those events often read with numbers similar to the numbers similar to the coordinates mouse is about to jump to. Each jump happens a fraction of a second after I've started dragging, and in each drag, the mouse usually jumps from one to three times, seemingly by three fifths each time. I can apparently delay the effect for more than a second by starting the drag motion and stopping (with the button held down) immediately after the dragged icon clone appears, but when I resume mouse movement, the mouse immediately teleports 3/5ths of the way leftward (even across the multiple monitors). It tends to jump more than once before stopping if I continue moving the mouse in a slow or smooth motion.
Hint: I've recently set up a touchscreen monitor (Planar PCT2485), so I'm sure the act of setting it up may have something to do with it, but this ONLY happens when a mouse button is depressed (or software is emulating the mouse being depressed). Nothing has been touching the touchscreen. The touchscreen is powered off and LITERALLY unplugged when this happens, though it also happens when the screen is on. My two main monitors (both Dell up2414q, positioned left and center) are both running at 4K, and the touchscreen (on the right) is 1080p. Now that the touchscreen is calibrated properly, I don't want to have to type xrandr ever again. Please don't make me do it!
Hint 2: This doesn't always happen when clicking and dragging: I can consistently click and drag a tab in Chrome or Sublime Text 2, or drag a selection box around icons on the desktop or in Nautilus just fine, and I can resize any window, highlight any text, or drag any scrollbar with no problem. However, clicking and dragging a tab in Firefox or Atom, dragging a selection or image out of ANY browser window, or moving an icon or icon group on the desktop, Nautilus, or Filezilla will consistently result in the teleporting behavior, regardless of which screen I start on, or how far from the left edge of the leftmost screen I am.
Ubuntu 16.04 LTS 64-bit