This bug has been driving me a bit mad but I finally found something that claims to have a fix for it. The problem is where an entry’s permalink gets a “_1″ (underscore and a 1) appended to the end of the files name when you edit something in the post. This obviously breaks anyone who linked to the entry that didn’t have the _1 suffix (well, not really, but it does send them to the entry that doesn’t include your latest edits).

This link to the Movable Type forums addresses the issue.