Squeak,
I heard back from Yamaha and they compared the 540 and the 550 and could not find any difference in the way the style recording works. Both models default to 2 measures when they erased all tracks and all sections. They agreed with me that you need to clear each section as you wish to record and then you will have your 4 measure loops.
Good Luck!
George Kaye
Kaye's Music Scene