Steps to reproduce:
1. 
2. 
3. 


Stack trace:
(gdb) bt

+ Trace 210135

$6 = (CamelObjectEventHookFunc) 0xb7e39680 <folder_changed>
(gdb) p *$6
$7 = {void (CamelObject *, gpointer, gpointer)} 0xb7e39680 <folder_changed>
(gdb) p obj
$8 = (CamelObject *) 0x84b9d08
(gdb) p *$8
$9 = {klass = 0x850a118, magic = 2007188717, hooks = 0x843d558, 
  ref_count = 13, flags = 0, next = 0x84b9c90, prev = 0x84b9d80}
(gdb) p event_data
$10 = (void *) 0x8509448
(gdb) p pair->data
$11 = (void *) 0x8d3f4e0
(gdb) 

Other information:
When I killed and restarted the app, and did the same thing, there was no problem.
I also do have a core file around if anybody is interested.