Trackback changes xhtml tags

I’ve got three trackbacks to one article,
1. blog xhtml1 strict- trackback per *textfield*
2. blog transitional – trackback per *automatic*
3. blog transitional-trackback per *textfield*

the html tags of the 3rd blog -only the first sentence – change to pre and code inclusive entities

I’ve found a workaround per css -because my design looks very *fantastic* after this trackback of the 3rd blog.

but i can’t understand how can html tags change?

my knowldge about the trackback technic isn’t good enough to understand why this could happened.

any idea – or answer – or …?
thanks a lot
Monika

edit: the link to my article about this problem, but it is in german
https://www.webdesign-in.de/index.php/mts/trackback-design-probleme-und-eine-loesung/