There are some bugs in the RadRotator control in Q1 2010 and previous version related to onMouseOver event.
The problem appears , because the event is triggered twice. From what you are saying the problem looks the same and you can easily identify it using FireBug or IE developer tools. This issue has been fixed in Q2 2010 or RadControls for ASP.NET AJAX. There will be a SP 4 of Sitefinity 3.7 where we will include Q2 2010. The SP will be released within 2-3 weeks. Alternative option would be using JQuery plugin to rotate your data.
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