That's a great question. I'll going to forward this over to our Book Tech staff to look into.
You can reach them directly for any other questions you may have about the book at firstname.lastname@example.org.
O'Reilly Media Customer Service Team
It appears that's the way that the Nook works. Here is a discussion on some ways to force it to be one column by adjusting font sizes -
Here is a different solution -
I hope that helps,
O'Reilly Book Support
Hm .... I would like to suggest that O'reilly should have a look on the epub books from Pragmatic Bookshelf.
Their book works correctly in landscape mode in the nook tablet.
Personally, the quality of epub books (pdf is beautiful and great) is not as good as Pragmatic Bookshelf. Take a look on the Erlang Programming from O'reilly, the source code font size is even bigger that the font size of normal text!
Don't get me wrong, I love books from Oreilly and the content quality is professional. But I would like Oreilly have better support on small device using epub.