checkout -m dumping core

git version 1.6.6.78.gbd757c

HEAD points to a non-existent branch refs/heads/master. Normal checkout 
origin fails with:
error: Entry '.cvsignore' would be overwritten by merge. Cannot merge.
(the working tree does indeed contain this file). So I tried checkout -m 
and git crashed. Workaround for me was reset --hard origin; checkout 
origin. I have the repository backed up in case someone wants to try 
themselves.

$ gdb `which git`
GNU gdb 6.8
Copyright (C) 2008 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later 
<http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
and "show warranty" for details.
This GDB was configured as "i386-pc-solaris2.11"...
(gdb) run checkout -m origin
Starting program: /export/home/tomc/local/git/bin/git checkout -m origin
warning: Lowest section in /lib/libpthread.so.1 is .dynamic at 00000074

Program received signal SIGSEGV, Segmentation fault.
0x080788fa in cmd_checkout (argc=0, argv=0x8047538, prefix=0x0) at 
builtin-checkout.c:450
450                             merge_trees(&o, new->commit->tree, work,
(gdb) list
445                             ret = reset_tree(new->commit->tree, 
opts, 1);
446                             if (ret)
447                                     return ret;
448                             o.branch1 = new->name;
449                             o.branch2 = "local";
450                             merge_trees(&o, new->commit->tree, work,
451                                     old->commit->tree, &result);
452                             ret = reset_tree(new->commit->tree, 
opts, 0);
453                             if (ret)
454                                     return ret;
(gdb) p o
$1 = {branch1 = 0x8047650 "origin", branch2 = 0x0, subtree_merge = 0, 
buffer_output = 1, verbosity = 0, diff_rename_limit = -1, 
merge_rename_limit = -1, call_depth = 0, obuf = {alloc = 0, len = 0, buf 
= 0x81643ac ""}, current_file_set = {
     items = 0x0, nr = 0, alloc = 0, strdup_strings = 1}, 
current_directory_set = {items = 0x0, nr = 0, alloc = 0, strdup_strings 
= 1}}
(gdb) p new
$2 = {name = 0x8047650 "origin", path = 0x8166438 "refs/heads/origin", 
commit = 0x8168f48}
(gdb) p work
$3 = (struct tree *) 0x8174f90
(gdb) p old
No symbol "old" in current context.
(gdb) p result
$4 = (struct tree *) 0xfefc81be
(gdb)