Comment 2 for bug 1198844

StacktraceTop:
 g_type_check_instance_cast (type_instance=type_instance@entry=0xb892a388, iface_type=3099208552) at /build/buildd/glib2.0-2.37.3/./gobject/gtype.c:4009
 on_properties_changed (interface=0xb8c6b2d0, changed_properties=0xb8901720, invalidated_properties=0xb8b7f880, user_data=0xb892a388) at diagnostics-widget.c:149
 ffi_call_SYSV () at ../src/x86/sysv.S:65
 ffi_call (cif=cif@entry=0xbfc49314, fn=0xa56bbd00 <on_properties_changed>, rvalue=0xbfc492a0, avalue=avalue@entry=0xbfc49260) at ../src/x86/ffi.c:411
 g_cclosure_marshal_generic (closure=0xb8bb0960, return_gvalue=0x0, n_param_values=3, param_values=0xbfc49480, invocation_hint=0xbfc4942c, marshal_data=0x0) at /build/buildd/glib2.0-2.37.3/./gobject/gclosure.c:1454