Why is uilistbox Multiselect property being ignored inconsistently?

I am using the new App Designer in 2016a and have created a uilistbox. The Multiselect property is set to 'on'. When running with a debug flag set multi-selection works, when running normally multi-selection does not work. What is driving this behavior? Are there any workarounds or solutions?

Auto generated code that creates the list box:

app.DaysimeterList = uilistbox(app.HomeTab);
app.DaysimeterList.Items = {'proto 1', 'proto 2'};
app.DaysimeterList.Multiselect = 'on';
app.DaysimeterList.ValueChangedFcn = createCallbackFcn(app, @DaysimeterListValueChanged);
app.DaysimeterList.Position = [526 83 100 299];
app.DaysimeterList.Value = {'proto 1'};

Code that updates the list and is supposed to select all items:

function results = refreshDaysimeterList(app)
  daysimeterPaths = app.getDaysimeters;
  deviceSns = cellfun(@app.getDeviceSn,daysimeterPaths,'UniformOutput',false);
  app.DaysimeterList.Items = deviceSns';
  app.DaysimeterList.ItemsData = daysimeterPaths';

    if isempty(daysimeterPaths)
      app.DaysimeterList.Enable = 'off';
      app.DaysimeterList.Items = {'None'; 'detected'};
    else
      app.DaysimeterList.Enable = 'on';
      app.DaysimeterList.Value = app.DaysimeterList.ItemsData(:); % Select all Daysimeters
    end
  end

The update function is called during the App startup:

% Code that executes after component creation
function startupFcn(app)
  app.loadPreferences; % Load the App preferences
  app.refreshDaysimeterList; % Refresh the Daysimeter list
end

[Chris Portal]

Clarifying question...when you say you're "running with a debug flag", are you referring to running with an Editor breakpoint? If so, if you put something like "pause(0.2)" at the end of your startupFcn, and run normally without any breakpoints, does it resolve the problem?

[Meade]

The "Value" method is usually indices, but you're trying to assign it whatever format "ItemsData" is in.

Try changing the last line in your refreshDaysimeterList fnc.

app.DaysimeterList.Value = 1:numel(app.DaysimeterList.ItemsData); % Select all Daysimeters

Does this change your result?

[Greg]

The comment by Meade is completely off the mark. AppDesigner documentation clearly states that the 'Value' property is a value of the 'ItemsData' property, or of 'Items' if 'ItemsData' is empty.