So it wasn't 'just me'
Within a week of installing calibre almost 6 years ago I spotted the ISO option for formatting datetime columns. That'll do me I said to myself. But, when I tried to edit dates I ran up against the problems recently reported
here 
I decided it had to be what I was doing. At that time I was struggling with the metadata edit screen and that darn calendar widget. So I used the same workaround as the launchpad error reporter.
But
this post by chaley raises a question that been on mind ever since 2012: "Why do dates in calibre record the timezone."
Rather than make QDateEdit timezone aware as chaley 'suggests'
could be done, why not make calibre timezone neutral/agnostic/ignorant. The only datetime calibre records that reflects a realtime event is the non-editable metadata last_modified, the other two and custom column dates have arbitrary values set by the user. Under what circumstances would a user want to record the UTC offset of the datetime they are entering.
BR