I've found a problem with editing the appearance of a button bar with a file created in 14 and a brand new file created in 16 in FMPA 16.0.2 on OS X 10.11.4
1) Select the button bar and type Cmd-3 to go to the Appearance Inspector.
2) Select the 'Button Bar' pop-up menu and choose 'Button Bar: Segment'
The 'Fill' and 'Line' attributes are inactive.
3) Select the 'Button Bar: Segment' and choose 'Button Bar: Divider' and immediately change back to 'Button Bar: Segment'.
Sometimes the 'Fill' and 'Line' attributes are active, but this is not consistent, sometimes it takes selecting another menu item and going back to 'Button Bar: Segment' a couple of times before the attributes become active.