Hello Nguyen,

Thank you for reporting the behavior. The reason for it is because when you change the widget's value and the dropdown is closed, the filter input field is being cleared. Then, upon re-opening the dropdown, the page will not be the same as the one on which the selected item is, so a read request will be made to the server to retrieve the correct page and items. Then, upon closing, the widget considers that the change event should be triggered.

That is not expected as behavior in this scenario, so I am converting this thread to a bug report. You can find it in our Feedback Portal on this link. 

Note that the behavior will not occur if you remove the valueMapper, as we support virtualization without it. You can refer to this thread for further information. So you can remove it if you do not wish the change event to be triggered twice.

I am updating your Telerik Points as a small token of gratitude.

Feel free to contact us whenever you have other questions.

Regards,
Martin
Progress Telerik