Sorry for the late reply on this, but I only now got a chance to (try to) update
to mandoc-1.14.5.
gdb> bt
#0 0x0000000000459eab in raise ()
#1 0x000000000040122a in abort ()
#2 0x0000000000401104 in __assert_fail_base.cold.0 ()
#3 0x00000000004550c2 in __assert_fail ()
#4 0x0000000000404444 in print_text (h=0x149e470, word=0x516d370 "delta(disk.dev.total_bytes) / delta(disk.dev.total)") at html.c:809
#5 0x000000000040a405 in roff_html_pre_ce (h=0x149e470, n=0x3136bc0) at roff_html.c:77
#6 0x000000000040a369 in roff_html_pre (h=0x149e470, n=0x77b8120) at roff_html.c:61
#7 0x0000000000404ec9 in print_man_node (man=0x149e2d0, n=0x77b8120, h=0x149e470) at man_html.c:221
#8 0x0000000000404c93 in print_man_nodelist (man=0x149e2d0, n=0x77b8120, h=0x149e470) at man_html.c:156
#9 0x0000000000404fb5 in print_man_node (man=0x149e2d0, n=0x833a300, h=0x149e470) at man_html.c:234
#10 0x0000000000404c93 in print_man_nodelist (man=0x149e2d0, n=0x833a300, h=0x149e470) at man_html.c:156
#11 0x0000000000404fb5 in print_man_node (man=0x149e2d0, n=0x2127fb0, h=0x149e470) at man_html.c:234
#12 0x0000000000404c93 in print_man_nodelist (man=0x149e2d0, n=0x2127fb0, h=0x149e470) at man_html.c:156
#13 0x0000000000404fb5 in print_man_node (man=0x149e2d0, n=0x382a510, h=0x149e470) at man_html.c:234
#14 0x0000000000404c93 in print_man_nodelist (man=0x149e2d0, n=0x382a510, h=0x149e470) at man_html.c:156
#15 0x0000000000404fb5 in print_man_node (man=0x149e2d0, n=0x8a00e80, h=0x149e470) at man_html.c:234
#16 0x0000000000404c93 in print_man_nodelist (man=0x149e2d0, n=0x8a00e80, h=0x149e470) at man_html.c:156
#17 0x0000000000404ba9 in html_man (arg=0x149e470, man=0x149e2d0) at man_html.c:134
#18 0x000000000041c176 in process (parser=0x149db80, outtype=OUTT_HTML, formatter=0x149e470) at mandocd.c:271
#19 0x000000000041bfab in main (argc=1, argv=0x7fffa4b775e8) at mandocd.c:214