ExtJS border layout split resize doesn't work!

I have a border layout with a grid and a panel, the grid is in 'center', the panel is in 'south'.

The handle to resize the regions appears to work, but upon releasing the mouse, no change occurs, and the panels remain where they are.

var content = new Ext.grid.GridPanel({
                                  id: 'bug-grid',
                                  border: false,
                                  view: new Ext.grid.GroupingView(),
                                  region: 'center',
                                  plugins: [filters],
                                  store: bugStore,
                                  colModel: columnModel,
                                  trackMouseOver:false,
                                  loadMask: true,
           开发者_StackOverflow社区                       sm: new Ext.grid.RowSelectionModel({singleSelect:true}),
                                  listeners: {
                                      rowclick: {
                                          fn: function(grid, rowIndex, event) {
                                              var bug_id = grid.store.getAt(rowIndex).id;
                                              Ext.getCmp('activity-panel').load(activity_lines_path(bug_id));
                                          }
                                      }
                                  },
                                  bbar: new Ext.PagingToolbar({
                                                                  plugins: [filters],
                                                                  pageSize: pageSize,
                                                                  store: bugStore,
                                                                  displayInfo: true,
                                                                  displayMsg: 'Displaying bugs {0} - {1} of {2}',
                                                                  emptyMsg: "No bugs to display"
                                                              })
                              });
var activity = new Ext.Panel({
                                 id: 'activity-wrapper-panel',
                                 region: 'south',
                                 items: getActivityPanel(),
                                 autoHeight: true,
                                 bodyBorder: false,
                                 border: false
                             });
var page = new Ext.Panel({
                             id: 'page',
                             layout: 'border',
                             defaults: {
                                 split: true,
                                 frame: true
                             },
                             items: [content, activity],
                             renderTo: 'application',
                             height: 800
                         });

I had autoHeight: true set, where they shouldn't have been. Removing that fixed the issue.