It's not an issue with the 505, this is expected behavior. When you zoom in on PDF, to contents are "reflowed" - essentially stripping a lot of the formating so we can enlarge the font sizes. Because of technical limitations with PDF files (and the current implementation of the reflow algorithms), we do not reflow across pages, so you will get gaps between pages.
Also because of limitations with with the PDF file structure itself (it is not an easily reflowable content), line breaks will appear in odd places.
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Jim Lester
Adobe Systems