Minimum Margins in eBook Viewer Cause Bad Layout in some ePubs

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The minimum margin size in the eBook viewer is set to 10 for each of side, top, and bottom. With some eBooks with background images, this results in the text being shifted far down the page (and off below the bottom of the background image). Modifying the config.ui and config_ui.py files in src\calibre\gui2\viewer to allow minimum margins of -1000 fixed this problem.
This suggests that these books might use negative margins to align text with the background image; alternatively, perhaps this is not the best fix and there is some other error in the ePub parser causing these alignment problems.

Example input causing this problem can be found here:
http://bit.ly/2pXNUsX

[Kovid Goyal (kovid)]

That is a so-called "Fixed layout EPUB" these are not supported in calibre.