Hello Odd Veibust,
I am not exactly sure how the "checkboxes" logic interferes the DropDownList data state (probably the data is filtered on server and widget is not notified), but if you would like to retrieve the data on open then you can wire the open
event [ .Events(e => e.Open("open")); ] and call the data source read
method to force server request:
Let me know if I am missing something.
Check out the Telerik Platform - the only platform that combines a rich set of UI tools with powerful cloud services to develop web, hybrid and native mobile apps.