new firmware 5.19.656: eink-reader crashes?

I've updated my Touch HD2 to the last firmware a few days ago, and am surprised to find that various of my epubs crash the builtin reader. I cannot pinpoint the very latest firmware, but to the best of my memory, I had no earlier problem with those particular ones. And the release notes spell "Fixed: 1. Inability to open some EPUB books" - which sounds suspicious...
It may well be my device, but I note that I have still 2.5GB free on /ext1, ad that a factory reset did not help (it trashed all my neat added apps and dictionaries, though... :smack:)

Could someone test some of these epubs on their devices with older or newest FW and report?

https://www.gutenberg.org/ebooks/48913
https://www.gutenberg.org/ebooks/44549
https://www.gutenberg.org/ebooks/53768

Choose epub with images please. Try to navigate to some page in the middle of the book. To me, that simply quits the reader. Each book seems to have a point beyond which the reader gives up. Coolreader instead copes with them normally.

Those books are produced with the PG toolchain, which should be a guarantee of sanity. I actually coded them and have had fine control on the html. They are medium sized, but no way monsters. Understanding what's wrong may provide feedback to PB, or help me produce better books for PG.

Thanks, Enrico