I have spent whole day in trying to fix my custom ButtonBar skin since it was impossible to correctly allign fxg background graphichs, an icon and the label in the skin. In the end of the day, I was hopelessly trying every possibility and suddenly I discovered it was all because of ButtonBarHorizontalLayout placed in the Datagroup of ButtonBar skin! After I replaced it with HorizontalLayout, everything worked as expected. There must be something totally wrong with this ButtonBarHorizontalLayout definition and I dont know what...
According to the documentation ButtonBarHorizontalLayout:
"The ButtonBarHorizontalLayout class is a layout specifically designed for the Spark ButtonBar skins. The layout lays out the children horizontally, left to right.
The layout attempts to size all children to their preferred size. If there is enough space, each child is set to its preferred size, plus any excess space evenly distributed among the children.
If there is not enough space for all the children to be sized to their preferred size, then the children that are smaller than the average width are allocated their preferred size and the rest of the elements are reduced equally.
All children are set to the height of the parent."
Does this documentation explain the issues you ran into?