This bug was detected by keytest, feel free to close if it is not helpful. 

Keycodes: 
'''KO: \AinKO: \C\[Escape]'''\[!Loop]
To reproduce:
1) Press Alt-I, N to open "Paste Defined Names" dialog (KO: \Ai)(KK: n)
2) Press Escape to close dialog (KO: \C\[Escape])
3) Go back to 1 (Loop)

I then get the following warnings in valigrind:

==12960== Memcheck, a memory error detector
==12960== Copyright (C) 2002-2009, and GNU GPL'd, by Julian Seward et al.
==12960== Using Valgrind-3.6.0.SVN-Debian and LibVEX; rerun with -h for copyright info
==12960== Command: /usr/local/bin/gnumeric
==12960== 

** (/usr/local/bin/gnumeric:12960): WARNING **: Running under buggy valgrind, see http://bugs.kde.org/show_bug.cgi?id=164298
==12960== Invalid read of size 4
==12960==    at 0x4EFE1A1: cb_free_keyed_dialog_context (in /usr/local/lib/libspreadsheet-1.10.14.so)
==12960==    by 0x81EA8F1: g_datalist_clear (in /lib/libglib-2.0.so.0.2400.1)
==12960==    by 0x79775A3: g_object_unref (in /usr/lib/libgobject-2.0.so.0.2400.1)
==12960==    by 0x5D2571A: gtk_main_do_event (gtkmain.c:1647)
==12960==    by 0x626886B: gdk_event_dispatch (gdkevents-x11.c:2372)
==12960==    by 0x81FF8C1: g_main_context_dispatch (in /lib/libglib-2.0.so.0.2400.1)
==12960==    by 0x8203747: ??? (in /lib/libglib-2.0.so.0.2400.1)
==12960==    by 0x8203C54: g_main_loop_run (in /lib/libglib-2.0.so.0.2400.1)
==12960==    by 0x5D25BB6: gtk_main (gtkmain.c:1219)
==12960==    by 0x404D0F: main (in /usr/local/bin/gnumeric-1.10.14)
==12960==  Address 0xf938ee8 is 24 bytes inside a block of size 32 free'd
==12960==    at 0x4C270BD: free (vg_replace_malloc.c:366)
==12960==    by 0x81EB46D: g_datalist_id_set_data_full (in /lib/libglib-2.0.so.0.2400.1)
==12960==    by 0x4EFE1E4: cb_free_keyed_dialog_context (in /usr/local/lib/libspreadsheet-1.10.14.so)
==12960==    by 0x81EB286: g_datalist_id_set_data_full (in /lib/libglib-2.0.so.0.2400.1)
==12960==    by 0x4EFF030: gnumeric_keyed_dialog (in /usr/local/lib/libspreadsheet-1.10.14.so)
==12960==    by 0x4FD1DA1: name_guru_init (in /usr/local/lib/libspreadsheet-1.10.14.so)
==12960==    by 0x4FD2070: dialog_paste_names (in /usr/local/lib/libspreadsheet-1.10.14.so)
==12960==    by 0x79755DD: g_closure_invoke (in /usr/lib/libgobject-2.0.so.0.2400.1)
==12960==    by 0x7989597: ??? (in /usr/lib/libgobject-2.0.so.0.2400.1)
==12960==    by 0x798AA75: g_signal_emit_valist (in /usr/lib/libgobject-2.0.so.0.2400.1)
==12960==    by 0x798B032: g_signal_emit (in /usr/lib/libgobject-2.0.so.0.2400.1)
==12960==    by 0x5C66262: _gtk_action_emit_activate (gtkaction.c:755)
==12960== 

Arch: x86_64
libgtk2.0-0:  2.20.1-0ubuntu2

I have not been able to reproduce the following bactrace manually, but keytest gives the following segmentation fault and backtrace.

Program received signal SIGSEGV, Segmentation fault.
0x00007ffff5086160 in g_type_check_instance_cast () from /usr/lib/libgobject-2.0.so.0

+ Trace 226585

For more info see the Keytest Report 
http://gmatht.homelinux.net/xp/keytest/html_out/out/gnumeric_3//html//1301882527.html