Note: Any button bar segment calculation that 1) uses a GET () that is record level relevant and 2) is in a portal, will not work - at least all those I have tried so far. For whatever reason, the segment calc looks at the layout base context and NOT the portal context. Pull the same calc outside the portal located button, and it works fine.
Also, button bar active states in a list view, highlights the button in every row. To resolve, set the button bar dialog's specify calculation to 1 (or true), and only the button the row being clicked, displays as active.
Any given button bar segment can be conditionally formatted individually, if the formula is set to TRUE. Makes it easy to hide icons, for instance, on selective buttons.