It sounds like the original ePub file had hardcoded the font sizes. Some folks use crappy apps to create ePub files. For example, MS Word is good for a self-contained document, but does a horrible job if you export a DOC file to HTML. MS Word, like most desktop word processors, wants to put a style on nearly every sentence in a document and this results in a huge overkill of styles that if converted to an ePub might result in hardcoded font sizes, font families, etc. I suspect the linux team didn't know squat about documentation and therefore created an extremely poorly formatted ePub from a DOC or some equally innappropriate format. When creating an ePub from scratch it is best to use an ePub creation tool or use simple HTML with as little CSS garbage as is possible.