Hi,
I came by a strange issue with epub generated using Calibre. If I enable hyphenation at Calibre viewer, it doesn't display well (weird spacing). Further details and screenshots are available at
https://github.com/GitbookIO/gitbook/issues/284 .
I can try tweaking the generator settings. It's also possible it's a viewer bug given the document displays well on native viewer of OS X. Any insight is welcome.