First of all, thanks for the plugin - it was working great until I made some changes to my site.
The link doesn't get written if it's coming from a custom field. I have a form that allows users to create a post and it takes the itunes link from a custom field and enters it into the post via my template. Any links created this way don't change. If I manually enter the link into the post then it works fine.
For now I've manually edited my template to add the code but I'd really like to figure out what's going on with the plugin and my setup.