I've seen that before--occurs when Twitter feed uses Twurl instead of Bitly. I have no idea why Twitterfeed is using Twurl. I've set it up to use my bitly account.
Shields down! Earth's mag field may drop in a flash: http://twurl.nl/v40ez3
Here's what twitterfeed says:
This happens when there is a temporary problem with shortening the URL using the preferred URL shortener - in a case like this twitterfeed will try a different shortener, on the basis that it's almost certainly preferable to post a link using a non-preferred shortener rather than not post a link at all.
So it should be a temporary issue and shortening should switch back to bit.ly next time (assuming whatever issue caused the API call to fail is fixed). If it does continue to be a problem please let me know.
AND on the problem with twurl links:
.... it seems the trailing slash in the URL is ignored when twurl shortens the link, which makes it not render (at least in the browsers I tested).
Hopefully this should be temporary and the links should go back to being shortened with tinyurl again, but if you can replicate the issue you may also want to report it to twurl themselves.