I really should have a keyboard shortcut for the following:

Without a sample of the offending epub to look at we here will just be guessing as to the problems associated with it as we can not see for ourselves what might be the matter. In this case my guess is that it is a grand rodent conspiracy between marmots, beavers and groundhogs to distract us from their schemes to take over the world.

Having said all that you are in luck as I suspect I do know what's "wrong" with your epub. I notice that the typeface in your JPEG example is fixed-spaced leading me to believe you epub is plain text file in disguise and that were we to look into it we'd find lots of paragraphs that look similar to <pre>This is the text.</pre> hence the rendering issues.

Any others willing to concur?