When we populate a Calendar with a number of events, only the first event appears initially.

However, if we click Next, followed by Previous, all of the events for the current Month appear.

I have created a small code snippet that reproduces the issue.
Simply load the module, only the first event appears, click Next, followed by Previous, then all events appear for the current month.

Code:
public class Sandbox2 implements EntryPoint {
    @Override
    public void onModuleLoad() {

        Window window = new Window();
        window.setWidth100();
        window.setHeight100();
        Calendar calendar = new Calendar();
        calendar.setShowDayView(Boolean.FALSE);
        calendar.setShowWeekView(Boolean.FALSE);
        calendar.setShowAddEventButton(Boolean.FALSE);
        calendar.setDisableWeekends(Boolean.TRUE);
        calendar.setShowDateChooser(Boolean.FALSE);
        calendar.setCanCreateEvents(Boolean.TRUE);
        calendar.setWidth100();
        calendar.setHeight100();
        window.addItem(calendar);
        window.show();

        HashMap<String, String> eventMap = new HashMap<String, String>();
        eventMap.put("2015-07-20", "Event1");
        eventMap.put("2015-07-21", "Event2");
        for (String dateStr : eventMap.keySet()) {
            DateTimeFormat dtf = DateTimeFormat.getFormat("yyyy-MM-dd");
            Date startDate = dtf.parse(dateStr);
            Date endDate = new Date(startDate.getTime() + 1);
            calendar.addEvent(startDate, endDate, eventMap.get(dateStr), null);
        }
    }
}
Using:
FF 24.8.1 ESR
SmartClient Version: SNAPSHOT_v10.1d_2015-07-16/Pro Deployment (built 2015-07-16)


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On a side note, it was working with the following build (this started when upgrading to 5.1).
SmartClient Version: v10.0p_2015-06-11/Pro Deployment (built 2015-06-11)