Sticky buttons - crumbs?
I also had a problem with the page-turn button sticking...and pages turning, turning, turning out of control. I think it may have been due to little crumbs getting in the cracks around the buttons....after I took a soft brush, and brushed around the buttons while holding the device up-side down - the problem went away! Maybe i should refrain from munching on cookies while reading!
Worth a try before returning your reader to Sony....