TextView AllowsReturn setter arbitrarily scrolls text out of sight

[tznind]

Describe the bug
When you set AllowsReturn the text you have set is scrolled completely out of the text views viewport leaving an empty text box. You have to press left to scroll the text back into focus.

To Reproduce

    [Fact]
    public void AllowsReturnShouldNotScrollView ()
    {
        var tv = new TextView ()
        {
            X = 1,
            Height = Dim.Fill (2),
            Width = Dim.Fill (2),
            Text =  "Heya",
            AllowsTab = false,
        };
        var top = new Toplevel ();
        top.Add (tv);

        tv.SelectAll ();
        Assert.Equal(1,tv.LeftColumn);
        tv.AllowsReturn = false;

// fails here
        Assert.Equal (1, tv.LeftColumn);
    }

Error is:

  Message: 
Assert.Equal() Failure: Values differ
Expected: 1
Actual:   5