I’m confused

Jazz Theory book on Nexus 7

I'm reading the Jazz Theory Book (which appears as an app) on a Nexus 7 and the page width isn't right. Gradually as I work through the book, the left hand margin decreases until the left of the text is no longer in view, and the next page edge is getting visible on the right side. Changing margins in the settings has no effect. Fault ?
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