DOCX Conversion - gitch
I've noticed some odd spans in the output of DOCX->EPUB Conversions - <span id="id_GoBack">. They don't have any effect on my viewing of the EPUB, but I only use the calibre viewer and the Simple Epub Extension for Chrome.
I am pretty sure they occur where I've corrected the DOCX - maybe the most recent correction. My guess is that they're something to do with Word's undo. could be since Word 2010, I upgraded from 2007 not so long ago.