The RadWatermarkTextBox control updates the position of the floating label when it gets/loses focus. This moves the label to the center or to the top based on whether the control is focused or is losing the focus. This is done via a method that is currently private. 

We can expose the method so that it can be used based on the client's logic.

Currently, the method can be invoked as follows:

Type radWatermarkTextBoxType = typeof(RadWatermarkTextBox);

MethodInfo handleLabelStateChangeMethodInfo = radWatermarkTextBoxType.GetMethod("HandleLabelStateChange", BindingFlags.NonPublic | BindingFlags.Instance);

if (handleLabelStateChangeMethodInfo != null)
{
    handleLabelStateChangeMethodInfo.Invoke(this.radWatermarkTextBoxInstance, new object[1] { false });
}

When the WatermarkBehavior is set to either HideOnTextEntered or HideOnClick, moving the focus with the Tab key will not move it on the first press.

To work this around, handle the PreviewKeyDown event and manually move the focus to the next element when the Tab key is the e.Key property's value.

When setting this property to CaretToEnd, a possible workaround which can be used is to subscribe to the GotFocus event of the control. In the event handler you can set the SelectionStart property to the length of the text using a Dispatcher.BeginInvoke() method.  

private void RadWatermarkTextBox_GotFocus(object sender, RoutedEventArgs e)
{
	var watermarkTextBox = sender as RadWatermarkTextBox;
	if(watermarkTextBox!= null)
	{	
		Dispatcher.BeginInvoke((Action)(() =>
		{
			watermarkTextBox.SelectionStart = watermarkTextBox.Text.Length;
		}));
	}
}

When click with mouse on the text it is selected every second time even when SelectionOnFocus is set to "SelectAll". If you click before the text it is selected every time.