I have this simple code checked this with 10.2 and 11.2 version both give wrong NewDate inside the events ( ActiveDayChanging and ActiveDayChanged events) when navigating dates (right left buttons).

WebDayView wdv = new WebDayView();
WebScheduleInfo wsi = new WebScheduleInfo();
WebDateChooser wdc = new WebDateChooser();

protected void Page_Load(object sender, EventArgs e)
{
wdc.ValueChanged += new WebDateChooser.ValueChangedEventHandler(wdc_ValueChanged);
wsi.ActiveDayChanged += new ActiveDayChangedEventHandler(wsi_ActiveDayChanged);
wsi.ActiveDayChanging += new ActiveDayChangingEventHandler(wsi_ActiveDayChanging);
wdv.EnableKeyboardNavigation = true;
  wdv.NavigationButtonsVisible = true;
wdv.WebScheduleInfo = wsi;
wdc.AutoPostBack.ValueChanged = true;
form1.Controls.Add(wdc);
form1.Controls.Add(wdv);
form1.Controls.Add(wsi);

}

void wsi_ActiveDayChanging(object sender, ActiveDayChangingEventArgs e)
{

}

void wsi_ActiveDayChanged(object sender, ActiveDayChangedEventArgs e)
{
wdc.Value = e.NewDate.ToString();
}

void wdc_ValueChanged(object sender, WebDateChooser.WebDateChooserEventArgs e)
{
wsi.ActiveDayUtc = new Infragistics.WebUI.Shared.SmartDate((DateTime)e.Value);
}