I didn't find anything relevant in a cursory search...
When importing a DOCX as a new book in calibre's editor, the epub is created with no version attribute in the opf package tag. Is this by design (or perhaps there's an option somewhere to pick which version you want)? The Check Book tool flags the missing version attribute, of course, but it can't be auto-fixed.
Importing HTML as a new book has the required package version attribute.
EDIT: updated to 2.76 (after making this post) just to make sure it hadn't already been changed/fixed. :o
When importing a DOCX as a new book in calibre's editor, the epub is created with no version attribute in the opf package tag. Is this by design (or perhaps there's an option somewhere to pick which version you want)? The Check Book tool flags the missing version attribute, of course, but it can't be auto-fixed.
Importing HTML as a new book has the required package version attribute.
EDIT: updated to 2.76 (after making this post) just to make sure it hadn't already been changed/fixed. :o