If the DataSource, to which the rotator is bound, is modified, then in order for the changes to be reflected in the rotator, you need to rebind the rotator on the server - that is, a postback or AJAX call is needed.
To update the rotator more smoothly, you could try configuring the timer to perform an AJAX request when a whole cycle has completed. Another idea is to do a pause for a while when a cycle has completed, and rebind the rotator during this pause. This way the user will know when the current loop of items has ended, and when the new starts.
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