thanks for the hint. I had a feeling it might be a scoping issue and tried assigning the handle to a WS variable, which seems to have been only half of the solution. I was able to use uipanels in place of the Empties successfully, though.
A great submission, very well structured. Great documentation, too.
I seem to have issues with using uiextra.Empy, though. when I put Empties in a VBox or HBox among other child elements, the empties vanish from the layout, either when I add more children or even when I do get(layout,'Children'). It's not that they are not displayed, they are actually gone and the layout changes.
The full problem is that I try to center a text uicontrol vertically, by putting it in a VBox Layout with an Empty above and one beneath it.