Originally Posted by theducks
It almost sounds like qxlooper is not converting the Sigil edited version of the EPUB (or is converting a different format to Mobi. Calibre remembers the LAST convert IN and OUT settings )
Be sure to drop the 'fixed' EPUB into the meta-data edit window, then pay close attention to the Source format setting, before clicking 'Convert'
You may be right. I always use the Open With GUI plugin
and right click to open the epub in Sigil. Doing this ensures I always save to my existing ePub in the calibre folder and never have to worry about a separate version of the ePub.