I am working with a fresh 3.5.1 install and a fresh 0.26 Image Rotator install. Every custom link I create is prepended with "%20" and, as a result, always results in a 'not found' error in my web browser.
For instance, if create a link to http://www.google.com, taking special care to make sure there is no whitespace before or after the link, the link in the image rotator will link to %20www.google.com. So, somewhere in the process, a non-breaking space is being added the beginning of the URL.
Automatically generated links (to the media page/uploads) do not have this issue.