D&D a HBox
D&D a Polygon shape into the HBox
Select the HBox and choose Menubar > Modify > Use Computed Sizes
Select the Polygon
Now resize the Polygon using the handles in the Content Panel - bug - the Hbox does not re-compute its size.

We have the same issue with the Arc and Text nodes. The problem seems to be related to the fact that when we resize these nodes using the handles we actually modify the ScaleX and ScaleY properties. This is problematic when you have a container with a mix of nodes. For example, I made a Hbox containing labels and using polygon shapes as visual separators between each label. Unfortunately as soon as I resized the polygons to my desired size the Hbox layout did not react as expected.