Originally Posted by HarryT
It probably means that the ePub has "hard coded" left alignment.
I agree. The 900 defaults to justified text alignment unless the ePub CSS specifies another alignment.
If you prefer left justification, you can use the Python scripts ineptepub.py and ineptkey.py (use Google to find info) to strip the DRM and then use calibre to make whatever changes you desire.
You can copy the ePub file and rename it to a zip file, then extract the zip file and search for any .CSS files. For example: Copy MyBook.epub to MyBook.zip then extract MyBook.zip into the folder MyBook. The CSS will show any hardcoded formatting. Search the CSS file(s) for strings like text-align: justify;
or text-align: left;
. If one or more of these strings are found, then text alignment is hardcoded in the ePub. Calibre can be used to override any CSS, but you have to know to do it.