How:
0) Open tbe
1) Add new toolbar
2) drag an item to it
3) drag it back to the tbe
-> toolbar is removed.

I only got this once while running under valgrind, couldn't reproduce it.

(epiphany:7988): Gtk-CRITICAL **: gtk_container_foreach: assertion
`GTK_IS_CONTAINER (container)' failed

==7988== Invalid read of size 4
==7988==    at 0x80CFE12: get_toolbar_nth (egg-editable-toolbar.c:168)
==7988==    by 0x80D1130: item_removed_cb (egg-editable-toolbar.c:884)
==7988==    by 0x80D8446: _egg_marshal_VOID__INT_INT (eggmarshalers.c:426)
==7988==    by 0x1BED02CD: g_closure_invoke (gclosure.c:437)
==7988==    by 0x1BEE0C3D: signal_emit_unlocked_R (gsignal.c:2435)
==7988==    by 0x1BEDFD85: g_signal_emit_valist (gsignal.c:2194)
==7988==    by 0x1BEE000A: g_signal_emit (gsignal.c:2238)
==7988==    by 0x80D3558: egg_toolbars_model_remove_item (egg-toolbars-model.c:685)
==7988==    by 0x80CFF54: drag_data_delete_cb (egg-editable-toolbar.c:210)
==7988==    by 0x1BEE1A6F: g_cclosure_marshal_VOID__OBJECT (gmarshal.c:636)
==7988==    by 0x1BED02CD: g_closure_invoke (gclosure.c:437)
==7988==    by 0x1BEE0C3D: signal_emit_unlocked_R (gsignal.c:2435)
==7988==    by 0x1BEDFD85: g_signal_emit_valist (gsignal.c:2194)
==7988==    by 0x1BEE00DF: g_signal_emit_by_name (gsignal.c:2262)
==7988==    by 0x1BB734ED: gtk_drag_selection_get (gtkdnd.c:3105)
==7988==    by 0x1BBDD933: _gtk_marshal_VOID__BOXED_UINT_UINT (gtkmarshalers.c:1338)
==7988==    by 0x1BED02CD: g_closure_invoke (gclosure.c:437)
==7988==    by 0x1BEE0C3D: signal_emit_unlocked_R (gsignal.c:2435)
==7988==    by 0x1BEDFD85: g_signal_emit_valist (gsignal.c:2194)
==7988==    by 0x1BEE00DF: g_signal_emit_by_name (gsignal.c:2262)
==7988==    by 0x1BC1CAEE: gtk_selection_invoke_handler (gtkselection.c:2060)
==7988==    by 0x1BC1B29B: gtk_selection_convert (gtkselection.c:790)
==7988==    by 0x1BB6F933: gtk_drag_finish (gtkdnd.c:748)
==7988==    by 0x1BB7065B: gtk_drag_selection_received (gtkdnd.c:1295)
==7988==    by 0x1BBDD7B1: _gtk_marshal_VOID__BOXED_UINT (gtkmarshalers.c:1261)
==7988==    by 0x1BED02CD: g_closure_invoke (gclosure.c:437)
==7988==    by 0x1BEE0C3D: signal_emit_unlocked_R (gsignal.c:2435)
==7988==    by 0x1BEDFD85: g_signal_emit_valist (gsignal.c:2194)
==7988==    by 0x1BEE00DF: g_signal_emit_by_name (gsignal.c:2262)
==7988==    by 0x1BC1CA6D: gtk_selection_retrieval_report (gtkselection.c:2025)
==7988==  Address 0x0 is not stack'd, malloc'd or (recently) free'd