pre causes problems

I had written this issue before and you were going to send me a code to fix this. The issue is: If a post starts with PRE, the preview page ignores this and word wraps the entire text. So, a web site with poems becomes unreadable because each poem starts with a PRE unfortunately.
(It was migrated from joomla and the migration tool “chose” to do it this way — or the original source contained all these PREs.)
Many thanks, tk

The page I need help with: [log in to see the link]