In the end, this is reduced too:
- epub and kepub handle cover in different ways
- Quality Check analyzes malformed (or possible PIA) epub
- You want that Quality Check analyze a specific case where a perfectly valid epub could generate a problematic kepub
This is not a bug at any side, it is a feature request for Quality Check epub. (Or, if you want the driver to modify this situation automatically when possible, a feature request for the driver).
A but is when a program doesn't do what it is specified to do, not when it doesn't what the user wants. It can sound pedantic to you, but it is a very very important difference in my world (software design).