I have found that when you make changes, particularly to tables, WYSIWYG editors seem to 'forget' to delete certain lines of code.
The < p > tag is often attributed to a css class when you copy & paste text into a table cell.
It looks neatly aligned in the editor, and if you preview in firefox, it is intelligent enough to know you have used a crap editor, and aligns things as you intended.
View it in Idiot Explorer however, and it will show up the flaws & will appear skew wiff.
Of the two best known, dreamweaver (IMO) is definately the best behaved, and you can go into code view & start learning how to handcode quite quickly, then use either method with just one editor