Font and line height changes when changing input formats

Using Suse 10.3, Marvin theme with no contributed modules.

All input formats mentioned below have all filter boxes checked and all possible users checked

Problem occurs when I change from Filtered HTML to Full HTML

I expected the font size and automatic line breaks to remain the same.

What happened was that in Full HTML page the font size becomes much smaller and there are no automatic line breaks. URLs are still converted though.

When I created a custom input format and viewed it, it was identical with the Filtered HTML page.

Is there a different CSS tag for Full HTML pages? If so they should be the same.

I have changed the CSS for page and comment fonts' size and family from the default but have noticed no problems except with the "Input formats" feature.