RSS limit parameter?

[Phil Barila]

When using the RSS feed, you can pass some parameters such as board=1 to the php script to limit the RSS to certain boards.  You can also pass a limit parameter to keep the new items list from getting too big.  However, it appears that when the limit is greater than the number of unread items, or possibly just some threshold that varies, the script returns nothing.
Example, mark all messages in the SlickEdit forum read, then try to load the following feed:
http://community.slickedit.com/index.php?type=rss2;board=1;limit=20;action=.xml
I would expect it to either return the most recent 20, or maybe "No new items."  Instead, it will sometimes return something that Firefox can't parse, which results in this:
about:livemark-failed