If I see a gap between two lines of text, and that gap vanishes when I commit the document to the web or save it to a file, then it’s not ‘WYSIWYG’. But this has been my experience with 100% of such editors.
I propose a new acronym to replace ‘wizzy-wig’:
WYSMBWYGIYLBIACWBFRTWNBMCTYSSIYUC
What You See Might Be What You Get if You’re Lucky but it Almost Certainly Won’t Be For Reasons That Will Never Be Made Clear to You So Suck it Ya Ugly Cunt
Not as pithy, but at least it’s accurate.
It sounds like you are only talking about html.
Delphi VB6 C# Winforms Qt
These wysiwyg editors usually worked/work without issues.