Triangulation lines visible in filled mesh after printing in matlab

(cross-posted in SO)

I've been using violin to generate (so-called) violin plots in matlab. The plot looks fine, but printing it to pdf results in a file where triangulation lines are visible...

Under the hood violin just uses fill() in a way which seems perfectly legit; a minimal, complete and verifiable example:

a=randn(10000,1);
[f, u, bb]=ksdensity(a,'bandwidth',0.2);
figure; fill([f'+i;flipud(i-f')],[u';flipud(u')],'b','FaceAlpha',1);
print(gcf,'-dpdf','a.pdf');

My version is R2017a.