Looking at it, you are only placing a simple nonbreaking space to the DOM, whereas I think it would expect something that can be added to the DOM.
You can try using <span> </span>
instead and see if that works.
But a better approach would be to use an empty spacer cell -- if you want padding between the matrixlayout columns -- or add some extra padding using the attachStyleClass
method -- if you want spacing between controls inside a column