Happens in both 1.9.0 (2004-03-25) and ruby 1.8.1 (2003-12-25).

Program received signal SIGSEGV, Segmentation fault.
0x080b0a34 in st_lookup (table=0x401f4d90, key=4369, value=0xbffef078) at st.c:258
258         hash_val = do_hash(key, table);
(gdb) bt
#0  0x080b0a34 in st_lookup (table=0x401f4d90, key=4369, value=0xbffef078) at st.c:258
#1  0x08053f03 in search_method (klass=1075482692, id=4369, origin=0xbffef0a4) at eval.c:378
#2  0x08053f59 in rb_get_method_body (klassp=0xbffef0e0, idp=0xbffef0e4, noexp=0x1111) at eval.c:399
#3  0x080544be in rb_method_boundp (klass=1075482692, id=4369, ex=0) at eval.c:585
#4  0x0805b075 in rb_respond_to (obj=0, id=0) at ruby.h:630
#5  0x4023d085 in rb_syck_output_handler (emitter=0x0, str=0x40241f70 "--- ", len=4) at rubyext.c:1243
#6  0x40237696 in syck_emitter_flush (e=0x4, check_room=0) at emitter.c:293
#7  0x4023d45e in syck_emitter_end_object (self=0) at rubyext.c:1393
#8  0x08069c31 in call_cfunc (func=0x4, recv=0, len=1075793296, argc=135254776, argv=0x401a9044)
    at eval.c:5348
#9  0x0805dec8 in rb_call0 (klass=1076012036, recv=1076770380, id=12417, oid=0, argc=0, argv=0x0,
    body=0x4022a288, nosuper=0) at eval.c:5479
#10 0x0805e0f8 in rb_call (klass=1076012036, recv=1076770380, mid=12417, argc=0, argv=0x0, scope=0)
    at eval.c:5696
#11 0x080591f2 in rb_eval (self=1076016916, n=0x0) at ruby.h:630

-- 
Running Debian GNU/Linux Sid (unstable)
batsman dot geo at yahoo dot com

People are going to scream bloody murder about that.
	-- Seen on linux-kernel