Edit only one post in a topic.

It seems I can only edit a single post per topic, and it's not always the latest one. I noticed a mispelling in a post of mine, but only the older post had the 'edit' link. I checked a few other threads and fouind that they only had 'edit' on the newest one. Kinda odd, but I'd sure like to be able to edit all my posts (well, not the first post of a thread I guess...) or if not, at least keep it the newest one.