Maybe you formatted the link incorrectly and Mudcat has some sort of filter that rejects anything that would totally mess up the rest of the page that followed the message.

The posting mechanism certainly seems to have some sort of damage limitation built in, so that html elements that are opened and not closed don't affect the rest of the page after the posting.

Did you test your posting in preview mode?
I always do that if it includes a link - it's so easy to get wrong.

Anahata