Alright, I got it to work by turning on auto line count and then clicking manual set up. I'm confused by the line count field... if it's just a total count of the number of lines of text, shouldn't it be read-only?
Unfortunately it seems to be even slower when using the auto pagination. I'm not sure it's working correctly - the behavior I see doesn't make sense to me: it creates a bunch of STM objects and each one has progressively fewer words than the last. So the rendered text only appears once, but the overall text seems to be duplicated a bunch across several STM objects.
To give a non-concrete example: if the original text is "One Two Three", then the first clone would have "Two Three", the second has "Three", and then there's a few empty ones as well.