In my development environment, I was experimenting with how quickly it takes winbind to notice when a domain controller cannot be reached, and how long it takes it to attempt to find and connect to another one, making sure 3.5.6 works properly. 
In doing so, I blocked via iptables connections to one of the DCs, and had to run an errand. I came back an hour later, logged into one of the test machines as a local user (ssh connection timed out) and winbind crashed. 

[2010/10/14 15:15:33.224948,  1] winbindd/winbindd_ads.c:126(ads_cached_connection)
  ads_connect for domain AWESOME failed: No logon servers
[2010/10/14 18:20:03.076780,  0] lib/fault.c:46(fault_report)
  ===============================================================
[2010/10/14 18:20:03.076935,  0] lib/fault.c:47(fault_report)
  INTERNAL ERROR: Signal 11 in pid 29111 (3.5.6)
  Please read the Trouble-Shooting section of the Samba3-HOWTO
[2010/10/14 18:20:03.077034,  0] lib/fault.c:49(fault_report)
  
  From: http://www.samba.org/samba/docs/Samba3-HOWTO.pdf
[2010/10/14 18:20:03.077194,  0] lib/fault.c:50(fault_report)
  ===============================================================
[2010/10/14 18:20:03.077259,  0] lib/util.c:1465(smb_panic)
  PANIC (pid 29111): internal error
[2010/10/14 18:20:03.158872,  0] lib/util.c:1569(log_stack_trace)
  BACKTRACE: 17 stack frames:
   #0 winbindd(log_stack_trace+0x1c) [0x2ac25c60102c]
   #1 winbindd(smb_panic+0x2b) [0x2ac25c6010fb]
   #2 winbindd [0x2ac25c5f108e]
   #3 /lib64/libc.so.6 [0x2ac25e9b52d0]
   #4 winbindd(winbindd_getdcname_recv+0xab) [0x2ac25c58421b]
   #5 winbindd [0x2ac25c53585c]
   #6 winbindd [0x2ac25c57da54]
   #7 winbindd [0x2ac25c560b86]
   #8 winbindd [0x2ac25c56049b]
   #9 winbindd [0x2ac25c58752d]
   #10 winbindd [0x2ac25c587ce1]
   #11 winbindd(run_events+0x182) [0x2ac25c6104c2]
   #12 winbindd [0x2ac25c610741]
   #13 winbindd(_tevent_loop_once+0x90) [0x2ac25c610b10]
   #14 winbindd(main+0x97e) [0x2ac25c536c0e]
   #15 /lib64/libc.so.6(__libc_start_main+0xf4) [0x2ac25e9a2994]
   #16 winbindd [0x2ac25c534609]
[2010/10/14 18:20:03.232683,  0] lib/fault.c:326(dump_core)
  dumping core in /var/log/samba/cores/winbindd

and in gdb a where shows:
(gdb) where
#0  0x00002ac25e9b5265 in raise () from /lib64/libc.so.6
#1  0x00002ac25e9b6d10 in abort () from /lib64/libc.so.6
#2  0x00002ac25c5f0b5d in dump_core () at lib/fault.c:337
#3  0x00002ac25c601139 in smb_panic (why=<value optimized out>) at lib/util.c:1481
#4  0x00002ac25c5f108e in fault_report (sig=1) at lib/fault.c:52
#5  sig_fault (sig=1) at lib/fault.c:75
#6  <signal handler called>
#7  0x00002ac25c58421b in winbindd_getdcname_recv (req=0x2ac25ce60a10, response=0x2ac25cea8930) at winbindd/winbindd_getdcname.c:86
#8  0x00002ac25c53585c in wb_request_done (req=0x2ac25ce60a10) at winbindd/winbindd.c:651
#9  0x00002ac25c57da54 in wb_dsgetdcname_done (subreq=0x2ac25cebd900) at winbindd/wb_dsgetdcname.c:100
#10 0x00002ac25c560b86 in wb_ndr_dispatch_done (subreq=0x2ac25ce5d490) at winbindd/winbindd_dual_ndr.c:135
#11 0x00002ac25c56049b in wb_child_request_done (subreq=0x2ac25ce5d550) at winbindd/winbindd_dual.c:170
#12 0x00002ac25c58752d in wb_simple_trans_read_done (subreq=0x2ac25ceced90) at ../nsswitch/libwbclient/wb_reqtrans.c:432
#13 0x00002ac25c587ce1 in wb_resp_read_done (subreq=0x2ac25ce82260) at ../nsswitch/libwbclient/wb_reqtrans.c:275
#14 0x00002ac25c6104c2 in run_events (ev=0x2ac25ce53330, selrtn=1, read_fds=0x7fffce6bdb20, write_fds=0x7fffce6bdaa0) at lib/events.c:148
#15 0x00002ac25c610741 in s3_event_loop_once (ev=0x2ac25ce53330, location=<value optimized out>) at lib/events.c:211
#16 0x00002ac25c610b10 in _tevent_loop_once (ev=0x2ac25ce53330, location=0x2ac25c97d8d7 "winbindd/winbindd.c:1275") at ../lib/tevent/tevent.c:497
#17 0x00002ac25c536c0e in main (argc=<value optimized out>, argv=<value optimized out>, envp=<value optimized out>) at winbindd/winbindd.c:1275