With v4 I've noticed a new behaviour within "Edit Metadata" as html-view.
From v4 on there seem to be additions to the html-text in form of cr/lf or cr or lf characters. In practice this looks like this:
"<div>
<p>some text</p>...."
In general, versions before v4 left any html-text untouched, i.e. the text above had looked like:
"<div><p>some text</p>...."
This behaviour attracted my attention because I filter off all unwanted tags or garbage out of descriptions with an external little helper - and explicitly this little helper strips any cr/lf combination out of descriptions (and unnessary blanks and whatnot).
But whenever I open up a sanitized description with the v4 versions the shown behaviour results.
(Generally, I wouldn't mind cr/lf whithin html-text - these are legal and allowed within html, so why shouldn't they show up within Calibre; but since my Kobo Aura HD read and displayed the descriptions without cr... and it saved a little space, I had removed them)