
The black stroke on the left is with a mouse, no pressure sensitivity, the red strokes on the right are with a Wacom tablet with pressure sensitivity enabled. All have these faulty paths where the cursor moved more slowly. It just goes crazy, getting all spiky and producing these weird holes.
I have checked that this isn't a problem of the fill rule; these are genuine defects in the paths. The above image is with fill-rule: nonzero - setting fillrule: evenodd creates more white areas where there is self-intersection (which is perfectly normal) but the defects above are not affected, they are actually part of the paths.
I have changed all settings for the Calligraphy tool but this issue persists.
The tablet works very well in general; in particular I don't have this problem with the vector calligraphy tool in Krita.
This makes the tool pretty much unworkable. I'm writing here in case there's something very obvious I'm missing here, and I really hope there is; if not I'll file this as a bug.
I am using Inkscape 0.92.1 r15371 on Ubuntu 17.04.