This is happening because you have passed selectedIndexes.
In the OnChange you should change the selected indexes to match the current index.

Here is the fixed version:
<DropDownList @ref=”EWDeviceList” SelectedIndexes=”@selectedIndexes” OnChange=”ChangeDevice” DataSource=”@dataSource”/>

DropDownList EWDeviceList = default!;

string[] dataSource = new string[] { “One”, “Two” };

int[] selectedIndexes = new int[] { 1 };

private async void ChangeDevice(Event chEv)
DropDownListChangeEventDetail detail = chEv[“Detail”];

selectedIndexes = new int[] { detail.Index };

string devNm = EWDeviceList.SelectedValues[0].ToString();


I hope this helps!

Best Regards,
Svetoslav Borislavov

Smart UI Team