I just finished creating my first plugin, and its for a client (took a full week for little money, but worth it to get that under my belt!).
It finally (after struggling with why get_post_meta wasn't working) works perfectly except for this little problem --- both the edit-pages and edit posts admin pages both now display both pages and posts.
In my plugin I used query_posts('post_type=any') to grab both pages and posts so I can grab the custom meta fields of each and produce an xml sitemap for videos. I assume this is why my problem with the admin pages comes up, but does any body know why?