Sourcelist doesn't display items

The sourcelist for the tweaks plug isn't displaying properly - see the attached image

relevant information:

(tweaks:21659): GLib-GObject-CRITICAL **: g_object_ref: assertion `G_IS_OBJECT (object)' failed

** (tweaks:21659): CRITICAL **: granite_widgets_source_list_data_model_add_children_monitor: assertion `item != NULL' failed

** (tweaks:21659): CRITICAL **: granite_widgets_source_list_expandable_item_get_children: assertion `self != NULL' failed

** (tweaks:21659): CRITICAL **: gee_iterable_iterator: assertion `self != NULL' failed

** (tweaks:21659): CRITICAL **: gee_iterator_next: assertion `self != NULL' failed

** (tweaks:21659): CRITICAL **: granite_widgets_source_list_expandable_item_add: assertion `self != NULL' failed

** (tweaks:21659): CRITICAL **: granite_widgets_source_list_expandable_item_add: assertion `self != NULL' failed

** (tweaks:21659): WARNING **: GnomeSettings.vala:73: No such file or directory

(tweaks:21659): GLib-CRITICAL **: g_variant_get_int32: assertion `g_variant_is_of_type (value, G_VARIANT_TYPE_INT32)' failed

(tweaks:21659): GLib-CRITICAL **: g_variant_get_int32: assertion `g_variant_is_of_type (value, G_VARIANT_TYPE_INT32)' failed

(tweaks:21659): GLib-CRITICAL **: g_variant_get_int32: assertion `g_variant_is_of_type (value, G_VARIANT_TYPE_INT32)' failed

(tweaks:21659): GLib-CRITICAL **: g_variant_get_int32: assertion `g_variant_is_of_type (value, G_VARIANT_TYPE_INT32)' failed

** (tweaks:21659): CRITICAL **: granite_widgets_source_list_expandable_item_expand_all: assertion `self != NULL' failed
[_LOG_LEVEL_INFO 01:35:36.066493] Switchboard.vala:592: Welcome to System Settings
[_LOG_LEVEL_INFO 01:35:36.066600] Switchboard.vala:593: Version: 0.9
[_LOG_LEVEL_INFO 01:35:36.066662] Switchboard.vala:594: Report any issues/bugs you mind find to lp:switchboard
[_LOG_LEVEL_INFO 01:35:36.259457] Application.vala:77: Switchboard version: 0.9
[_LOG_LEVEL_INFO 01:35:36.259491] Application.vala:79: Kernel version: 3.8.0-37-generic