Thank you, I changed the font to Optima from Thornburi
Good idea. Thonburi is a font dedicated for the Thai language, and using it for English may cause problems.
For example, "Geeza Pro" is listed in both the native app drop down menu (IBA) and iPad fonts list. But when I used it in my book and previewed it on the iPad, Geeza Pro didn't show. It was substituted with a different sanserif font.
Geeza Pro is only for use in producing Arabic language text.
There are many fonts for languages other than English available. Best not to use them for English.
(PS: It may seem like you are using Geeza Pro for English in OS X, but you are not, the OS automatically uses another font which does have Latin characters without telling you)