I was having a similar issue for a while. After many issues trying to copy and paste the buttons I wanted, I finally got them to paste! I'm not sure if it was an update/bug fix that helped me or pure perserverence, but checking out your answers definitely helped, so thank you.
However, now I'm having an issue where the buttons are misaligned with the slideshow whenever I try to preview it. The buttons are both evenly spaced to each side in Design mode, but as soon as I go to Preview, the buttons slide about 50 pixels to the right for some reason. I've tried pinning them, but that made the misalignment worse. The buttons work properly, but aren't in the right place. Please help!