Hint Assist not disappearing when Text value is set on MaterialDesignDataGridTextColumnPopupEditingStyle

I am creating dynamic columns for my DataGrid, so I am creating a number of MaterialDataGridTextColumn in code behind. I am modifying the MaterialDesignDataGridTextColumnPopupEditingStyle to allow the TextBox to have a hint property:

Style style = (Style)FindResource("MaterialDesignDataGridTextColumnPopupEditingStyle");
var editingStyle = new Style(typeof(TextBox), style)
{
	Setters =
	{
		new Setter(HintAssist.HintProperty, "Enter Score"),
		new Setter(MarginProperty, new Thickness(8)),
	}
};

foreach (string name in columnNames)
{
	var binding = new Binding("Attributes[" + name + "].Value")
	{
		UpdateSourceTrigger = UpdateSourceTrigger.LostFocus,
		ValidatesOnDataErrors = true,
		StringFormat = "0.0;;#"
	};

	var mdTxtCol = new MaterialDataGridTextColumn
	{
		Header = name,
		Binding = binding,
		EditingElementStyle = editingStyle,
		ElementStyle = centerTextSetter,
	};
	caseGrid.Columns.Add(mdTxtCol);
}

This successfully produces the pop up like so:

And as you type a value in the textbox, the hint property disappears, as it should:

However, the problem is that when this cell re-enters the edit mode while it contains a value, the hint property should disappear, but it doesn't:

As you can see, both the entered value and the hint property are shown.

Start by reproducing the issue with MaterialDataGridTextColumn, the MaterialDesignDataGridTextColumnPopupEditingStyle resource, and HintAssist.HintProperty as shown. Trace the TextBox hint behavior when editing begins with an existing value; done means the hint is hidden on re-entry while the value remains visible.