Jeannie,
It sounds to me like you have turned on a feature on all Yamaha keyboards called "one touch settings". If you have this button turned on (and you should see it in the display), everytime you change styles the right hand sound will change along with the style you have picked. If you turn of the OTS button, then you can change a style and the right hand sound will stay on whatever sound you are using.
Try this and look in your owners manual under one touch settings.
George Kaye
Kaye's Music Scene