Scans your RSS feed and ensures that every image has the correct alignment and margin settings.
This is usually due to caching. If you serve your feed via Feedburner or a similar service, it may take several hours before you'll see the changes. Also, most RSS readers will cache the feed and not show the updates immediately.
Probably not. In my experience the modified feed looks fine in Google Reader, and the W3C Feed Validator also says it's valid.