Trace:
======

0x000000000043bfa2 in km_dokey (menu=5) at keymap.c:519
519         while (LastKey > map->keys[pos])
    (gdb) backtrace
#0  0x000000000043bfa2 in km_dokey (menu=5) at keymap.c:519
#1  0x000000000043cad4 in km_error_key (menu=menu@entry=6) at keymap.c:850
#2  0x00000000004239f2 in mutt_index_menu () at curs_main.c:2702
#3  0x0000000000409256 in main (argc=1, argv=<optimized out>) at main.c:1297
    (gdb) next
521           if (pos > map->eq || !map->next)
    (gdb) next
519         while (LastKey > map->keys[pos])
    (gdb) next
521           if (pos > map->eq || !map->next)
    (gdb) next
519         while (LastKey > map->keys[pos])
    (gdb) next
521           if (pos > map->eq || !map->next)
    (gdb) next
519         while (LastKey > map->keys[pos])
    (gdb) next
521           if (pos > map->eq || !map->next)
    (gdb) next
519         while (LastKey > map->keys[pos])
    (gdb) next
521           if (pos > map->eq || !map->next)
    (gdb) next
519         while (LastKey > map->keys[pos])
    (gdb) next
521           if (pos > map->eq || !map->next)
    (gdb) next
519         while (LastKey > map->keys[pos])
    (gdb) next
521           if (pos > map->eq || !map->next)
    (gdb) next
519         while (LastKey > map->keys[pos])
    (gdb) next
    521           if (pos > map->eq || !map->next)
(gdb)

muttdebug:
==========

[snip]
[2016-04-12 19:01:08] 4< * 1271 FETCH (UID 7921 FLAGS (\Seen))
[2016-04-12 19:01:08] 4< * 1272 FETCH (UID 7922 FLAGS (\Seen))
[2016-04-12 19:01:08] 4< * 1273 FETCH (UID 7923 FLAGS (\Seen))
[2016-04-12 19:01:08] 4< a0006 OK Fetch completed (0.006 + 0.000 secs).
[2016-04-12 19:01:08] imap_open_mailbox: msgcount is 1273
[2016-04-12 19:01:08] Sorting mailbox...
[2016-04-12 19:01:09] Key is not bound.
[2016-04-12 19:01:09] Key is not bound.
[2016-04-12 19:01:09] Key is not bound.
[2016-04-12 19:01:09] Key is not bound.
[2016-04-12 19:01:09] Key is not bound.
[2016-04-12 19:01:09] Key is not bound.
[2016-04-12 19:01:09] Key is not bound.
[snip (continues like this forever)]