In the ribbon UI some commands are grouped in a "split button". From the help: "A split button keeps the information of the last called dialog from the ribbon button menu and calls it's action when the user presses on the left side of the icon. Pressing on the right side (the arrow) opens the ribbon button menu.".
In e.g. the measuring group, our users very often use the measure "distance surf to surf" command.
During the session the last used command is remembered, but in a new session it is lost. I think the last used command should be persistent.