Turning off text outline with VBA in PowerPoint

This is odd behaviour. I am trying to turn off the outline for text within a shape in PowerPoint 2013. To test the behaviour I added a simple text box to a blank slide, making sure it's selected. I then activate the text Format pane to observe the properties. I then turn on the outline programmatically in the VBE:

ActiveWindow.Selection.ShapeRange(1).TextFrame2.TextRange.Font.Line.Visible=msoTrue

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This works and I can now see the text outline on the slide and the corresponding properties in the Format pane.

But this doesn't turn the line off:

ActiveWindow.Selection.ShapeRange(1).TextFrame2.TextRange.Font.Line.Visible=msoFalse

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I've tried setting the Width to 0 and the Transparency to 1 but the Format pane still shows the line as Solid Line.

I suspect I'm looking at the wrong part of the object model as I also can't see the MsoLineFillType, which I need to access a gradient line fill.