Did you resolve your problem? I am having issues with tabbing as well.
You said you are using smart shapes. When I tried to use smart shapes as buttons, I found that although you can tab to them, you cannot select them be pressing Enter. If you want to select them with Enter, you'd have to put Enter as the shortcut key on each one, which doesn't make any sense because the user would never know which button would be activated when they press Enter.
So then I went back to buttons. It seemed that they were working but then all of a sudden, I started having the same problem. Enter would not select them. It was only after many tries and looking at someone else's program, I realized that it was because of the TYPE of button I was using - transparent buttons don't work. Image buttons and text buttons work.
Now the tabbing and press Enter works - except on a page where I have a video. While the video is playing, the focus stays in the browser menubar area and won't move to the presentatation window so tabbing doesn't work at all until the video finishes. I have been going crazy with this problem - I have posted a question about this but haven't received a response yet.