@davidfor/@GeoffR: Speaking of, I actually appear to have vanilla kepubs *without* those specific divs (and style-hacks, except for the .koboSpan thingy) [at least according to the liberated Kobo Desktop version of the file. The one on my H2O looks the same, but with it being encrypted, who knows]. Yet the book-inner/book-columns stuff is still mentioned in the js :?.
One common trait to those books is that they *already* wrap the full body in a single div (although not book-inner and/or book-columns). And I could swear those don't suffer from the cutoff bug.
Since I basically just threw myself in the deep-end of Kobo arcane stuff here, I'd be glad for some more feedback on that point
.