code: function _keyUp() {
              var filteredChoices;
  
              if (lxSelect.choicesViewMode === 'panes') {
                  filteredChoices = Object.keys(lxSelect.panes[(lxSelect.panes.length - 1)]);
              } else {
                  filteredChoices = $filter('filterChoices')(lxSelect.choices, lxSelect.filter, lxSelect.filterModel);
              }
  
              if (filteredChoices.length) {
                  lxSelect.activeChoiceIndex -= 1;
  
                  if (lxSelect.activeChoiceIndex < 0) {
                      lxSelect.activeChoiceIndex = filteredChoices.length - 1;
                  }
              }
  
              if (lxSelect.autocomplete) {
                  LxDropdownService.open('dropdown-' + lxSelect.uuid, '#lx-select-selected-wrapper-' + lxSelect.uuid);
              }
          }
docs: When the up key is pressed, select the previous item of the most right opened pane (the last one if we are at
  the top).