Screen Reading in Preview

I am getting very different screen reads when I test my screen reader on a slide in preview versus after it is published.

I am using the NVDA screen reader. If I publish the story in any format, the screen reader seems to behave as expected. If I preview a slide, however, I can only access the Keyboard-User functions (tab), but not the Screen Reader functions (up/down).

Can somebody clarify if this is the correct behavior? Do I have to publish a course before I can confirm that the screen reader has picked up the alt text and tab order correctly?

Thanks,

-Pierre