The problem with editing a post or saving a page is due to the fact that the function is being executed on the save function. scroll down to the last three lines and change:
add_action('save_post', 'ih_wp2punbb', 8);
to
add_action('publish_post', 'ih_wp2punbb');
edit: Wow, ok, I guess i should've tested this before commenting. Changing it from save_post to publish_post seems to make it still update whenever you update a post. Luckily, it doesn't post whenever you save a draft, though, because that would really suck. I'll be playing with this over the next couple days and post again when I figure out whats going on.