Mouse pointer moves at different speeds up/down and left/right in DOSBox

I'm trying to run a game* in DOSBox. It works perfectly except the pointer which moves at different speeds along y and x axes: it moves much more quickly up/down than left/right. Simply adjusting sensitivity in dosbox.conf always makes the pointer either move too fast up/down or too slow left/right.

Note that this is not the common issue of the pointer floating one direction or getting stuck in the corner. I can move it anywhere on the screen just fine but at different speeds. When I make a circle on the touchpad, the pointer moves mostly up and down, tracing a very thin and tall 0.

I tried disabling autolock, adjusting sensitivity, and disabling joystick to no effect. I am a noob to dosbox though so it's entirely possible I missed something obvious.

EDIT: Tested it with a USB mouse and it works fine so this is strictly a touchpad problem.

What else can I try? How do I make the pointer behaviour more intuitive?

* Constructor from GOG if it matters. I tried switching from the DOSBox they provide to the one installed with apt but it makes no difference.