The blogger html editor is wrong and has evil desires to follow compose mode actions.
Problem: blogger html/compose editor does not understand the css of the blog. So you can not preview your 'class' changes nor see the efects in Compose. Well, this is annoying by does not matter, I can use firebug for doing that and test the final look without publish it.
But where this 'feature' is annoying is in the <pre> vs css: white-space:pre;
If you have any text preformated but using a CSS class with "white-space:pre", that's ok and it works the first time. BUT.... if you try to edit it, it does not see any <pre> tag so it reformats the text and you loose all indentation!!!!