The second request in the described scenario is caused by the fact that when setting the value and the DropDownList is not yet populated, it will issue a query through the DataSource to populate itself. The DropDownList is not populate at this point as the response from the first request is not yet received. Usually this behavior is prevented by setting autoBind option of the DropDownList to false. Unfortunately, in the current version of MVVM this option will not take effect when widget is created declarative and the DataSource is a MVVM property. This we have already addressed, and the fix will be available in the internal builds and also with the next service pack.
the Telerik team
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