Different text-layout in Joomla frontend & editors view

Hello,
first I have to say this editor is very, very good.
Well, I am using Joomla 1.0.15 and JoomlaFCKeditor 2.6.1.
I have the BIG problem that i have different views of my text-input when being in 'Editor's view' and in 'Front end view'.
I made some screenshots - hoping you get an idea of the problem.

1. My JoomlaFCK options:

I choose 'P elements' both for 'Enter Mode' and 'Shift Enter Mode' because that's what Firefox AND Internet Explorer "understand" (both correctly show a line break).

2. Some text in the Joomla BACKEND = input in JoomlaFCK editor. The text says it all... then i saved the article.


3. Look at the Joomla Front end - everything looks good. The line break is shown.


4. Back in the BACKEND in JoomlaFCKeditor's view: any line break has gone. Although it's still correctly in the front end view of my site.


5. Now i turn on the sourcecode of the text - it looks OK since it got the line break.


5. After quitting the source-view the view of JoomlaFCKeditor my editor's view is all of sudden shown correctly - what I don't understand.


Now that is the problem: how can i manage to have the same, consistant view in Joomla-Front and Back end, view while writing an article?
Do I have to edit some FCK'S *.css file?

Thanks for your help/hints - this is pretty urgent

Greets
nuckel