Thank you so much, rashkae, pvs, and ChristopherTD! I just experienced this problem on a book I purchased today. Your posts pointed me in the proper direction to understand the issue with my book, which was the Kobo CSS and Javascript. I tend to agree with others that the book has been Koboized, and it is not the publisher's fault. If you are only reading on a Kobo, then you'll probably never know any different like those of us who buy Kobo Adobe EPUB's to read on non-Kobo ereaders. It's very interesting that Feedbooks has now written on this problem since Kobo has partnered with FNAC, a major retailer of French ebooks. That should get the issue more attention.
In my case, the font was super large and could not be modified smaller. Sorry but a dozen words on a page is just not readable for me! I have been purchasing books from Kobo since back when they were known as Shortcovers. Clearly, they have made changes recently. It appears to be only on books that have been published in the last few months. Very disappointing!
Kobo was a primary source of books for me, but now I will have to look elsewhere until they fix this problem. I'm also out $13 as I plan to re-purchase the book from another source since I really want this book as the publisher intended.
Anyway, search around on the internet or even in the other sub-forums on MobileRead like Sony and calibre, and you'll find other posts discussing this issue and how to fix it on your own if you don't want to repurchase the book.