How do fixed forced alignment in a Kindle book

Hi.

I have updated a book of mine that is available on the Kindle store. I have received a quality control message from Kindle that says

Quote:

"The body text in your book has forced alignment. It's important that your book file does not force alignment for body text."

I'm not sure what they are referring to exactly and their help page is lacking. Could it be page breaks?

The original version epub was converted with Kindlegen. I converted the second edition epub with Calibre. Does this have any bearing?