Book text size changes every two pages

On page 1 and 2 in a book there is large text on page 3 and 4 there is smaller text this repeats all through the book 

What I expected to happen was...

That the text would stay the same size on every page

What actually happened was...

The text changed size every two pages as described above

Steps to Reproduce:

1. get a book 
2. full the first page full of text
3. full the third page full of text

Variables:

colour:you will notice in the screen shot the text is coloured have tried without colour codes no luck

server:the screenshot was taken on my server however i tried on a offline world and still the same issue