https://bugzilla.redhat.com/show_bug.cgi?id=1437999
--- Comment #39 from Adam Goode adam@spicenitz.org --- I don't know the code well, but I suspect it's something in font_info_measure_font at https://github.com/GNOME/vte/blob/master/src/vtedraw.cc#L382
Also, it looks like this particular issue comes up from time to time. See https://bugzilla.gnome.org/show_bug.cgi?id=738781