When you try to add a value to a select box field where a default value is defined you end up with the following fatal error:

Fatal error: Call to a member function isHidden() on array in /usr/share/tuleap/plugins/tracker/include/Tracker/FormElement/Tracker_FormElement_Field_List_Bind.class.php on line 98
Call Stack
# Time Memory Function Location
1 0.0000 268808 {main}( ) ../index.php:0
2 0.0254 6525304 TrackerManager->process( ) ../index.php:33
3 0.0255 6525896 TrackerManager->processSubElement( ) ../TrackerManager.class.php:156
4 0.0302 6828184 Tracker->process( ) ../TrackerManager.class.php:139
5 0.0314 7196664 Tracker_FormElement_Field_List->process( ) ../Tracker.class.php:613
6 0.0314 7197040 Tracker_FormElement->process( ) ../Tracker_FormElement_Field_List.class.php:1392
7 0.0314 7197152 Tracker_FormElement_Field_List->processUpdate( ) ../Tracker_FormElement.class.php:218
8 0.0335 7403456 Tracker_FormElement_Field_List_Bind_Static->process( ) ../Tracker_FormElement_Field_List.class.php:1017
9 0.0446 7422384 Tracker_FormElement_Field_List_Bind->process( ) ../Tracker_FormElement_Field_List_Bind_Static.class.php:681
10 0.0462 7429936 Tracker_FormElement_Field_List_Bind->extractDefaultValues( ) ../Tracker_FormElement_Field_List_Bind.class.php:445
11 0.0462 7430504 Tracker_FormElement_Field_List_Bind_Static->filterDefaultValues( ) ../Tracker_FormElement_Field_List_Bind.class.php:467
12 0.0462 7430552 Tracker_FormElement_Field_List_Bind->getAllVisibleValues( ) ../Tracker_FormElement_Field_List_Bind_Static.class.php:940