Thanks to you both, and another question.
@robko - I'm sorry, I can't remember the details. I will do a full check and report it, but it's hard to summarise.
@tshering - I'm not sure if you're responding to my comments, but just in case... mine are ePub2 ebooks.
New question: Is it possible to read ePubs in landscape mode? I can't find any instructions on how to do that. It would be useful for reading long line poetry.