Here's the top of the backtrace.  (Thanks asmodai for helping me out with working out how to build a FreeBSD system ncurses with debugging information.)

#0  0x0000000801460714 in cannot_delete (win=0x80116b1d0)
    at /usr/src/lib/ncurses/ncursesw/../../../contrib/ncurses/ncurses/base/lib_delwin.c:54
        p = (struct _win_list *) 0xdbdbdbdbdbdbdbdb
        result = false
#1  0x0000000801460773 in delwin (win=0x80116b1d0)
    at /usr/src/lib/ncurses/ncursesw/../../../contrib/ncurses/ncurses/base/lib_delwin.c:71
        result = -1
#2  0x000000080170d140 in PyCursesWindow_Dealloc (wo=0x800eb74c0)
    at /usr/home/dickinsm/python/svn/trunk/Modules/_cursesmodule.c:357
No locals.
#3  0x000000000046325f in _Py_Dealloc (op=0x800eb74c0) at Objects/object.c:2211
        dealloc = 0x80170d110 <PyCursesWindow_Dealloc>
#4  0x00000000004578d8 in PyDict_DelItem (op=0x800f121b0, key=0x8011062e0)
    at Objects/dictobject.c:829
        mp = (PyDictObject *) 0x800f121b0
        hash = -3668919459648339544
        ep = (PyDictEntry *) 0x8010cb5a8
        old_value = (PyObject *) 0x800eb74c0
        old_key = (PyObject *) 0x8011062e0
        __func__ = "PyDict_DelItem"
#5  0x0000000000458a48 in dict_ass_sub (mp=0x800f121b0, v=0x8011062e0, w=0x0)
---Type <return> to continue, or q <return> to quit---
    at Objects/dictobject.c:1184
No locals.
#6  0x000000000041aadd in PyObject_DelItem (o=0x800f121b0, key=0x8011062e0)
    at Objects/abstract.c:205
        m = (PyMappingMethods *) 0x6c2960